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# What makes an inline 6 engine more reliable than a V6 or V8 configuration?3

## What makes an inline 6 engine more reliable than a V6 or V8 configuration?

(OP)
I don't want to start an engine debate but I know enough that generally straight 6 engines have a reputation for being more reliable than a V6 or V8 configuration. Just to simplify this discussion I want to stick with a discussion of older pre efi passenger vehicle and pickups engines because that is what I'm interested in. There aren't that many inline 6 engines out there but most of them have a very good reputation for being reliable.

-Cummins diesel all years but specifically the 89-98 "12 valves" are known to be very reliable
-Ford 300 straight 6 there are a lot of people including myself that would argue this is the most reliable gas motor ever produced
-Dodge 225 "slant 6"
-Jeep 4.0/4.2
-BMW inline 6
-Toyota supra inline 6
-HJ60 landcruiser diesel

Runners up:
-Toyota fj40 gas straight 6
-Mercedes 300D (inline 5 so doesn't get full credit)
-Chevy 250/292

These engines are often referred to as "bulletproof" or at the least are pretty well known for being very reliable. Especially when compared to their v6 or v8 counterparts.

Possible ideas that would contribute to the making them last longer than most V6 and V8s:

-less powerful so they aren't used as hard
-easier to access and work on therefore they are maintained better.
-less moving parts
-Power peaks at lower RPMs so it takes less to do more
-less prone to hot spots so less chance of detonation
-being upright gives more lubrication around the cylinder walls because gravity isn't working against the high side of the cylinder wall
-being upright applies the same theory for cooling and every other part where gravity could be fighting a v engine
-more bearings in the crankshaft (ford 300 has 7 main bearings)
-better balanced
-more surface area exposed to air and more open engine bay for it sheds heat better
-less nooks and cranies for old oil and engine particles to hide when the oil is being changed
-less parts of the engine hidden that aren't as well lubricated and/or cooled
-I don't believe any of the above mentioned engines have timing belts, it's either a chain or gears

If anybody has anything to correct or add feel free.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

Another engine is the Nissan RB series in the Skyline which has a very good reputation in street/racing applicatoins.

Just a guess, but I think the single head design offers a lot of bonuses. You have simpler cams/timing (timing belt for the RB series), intake, and exhaust. The harmonics of the inline six means it's very well balanced. I would guess that all those features results in an arrangement that is pretty solid and reliable comparatively, because there's less things to go wrong (and something always goes wrong).

Of course the biggest drawback is packaging. They fell out of favor because it takes up so much space, you can have a very good V8 in a smaller footprint.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

Where do you get that "general reputation"? There are plenty of current production automotive V6 engines that are extremely reliable. The reliability depends more on how well the design was done, how well the manufacturing was done, and how users use them, more than whether the cylinders are in a straight line or a V-configuration.

All of the factors that you give as an excuse for an inline engine being "more reliable" could equally apply to a V-configuration engine. The cylinder layout is irrelevant for that. (Most of your bullet points aren't accurate anyhow)

The Chrysler Pentastar 3.6 V6 in my van makes three times the power of an emission-strangled 225 Slant Six (displacement is almost the same) and meets emission standards that the old engine never could and uses less fuel than the old engine, and it weighs less, and it fits transversely which means the vehicle as a whole can weigh less, AND there is a fair chance that it will last longer with less fuss along the way. (So far, so good.) Sure, it's more complicated. But it's built to better tolerances and with better materials. It's got nothing to do with the cylinders being in a V or in a straight line. Technology has come a long way.

The old engine having less power meant that in a comparable application, the accelerator pedal was bolted to the floor ...

Now with that said, there are good and bad things about both.

The in-line engine allows for wider crank and rod journals. The V-configuration engine has two rod journals in the space where the in-line engine only needs one. This favors the in-line configuration in transport-truck engines.

But on the other hand, the long crankshaft of the in-line engine is more prone to torsional vibration.

The V-configuration engine requires two sets of cam drives if it is an OHC design. That favors in-line IF it will fit in the chassis. Transverse inline 6 is possible (it has been done) but it is hard to package.

Modern vehicles might be more tightly packaged and be more complex than they were in the old days ... but in the old days, cars were frequently junk after 60,000 miles. That's not the case any more, and at least in these parts, it's seldom an engine failure that sends it to the junk pile.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

When I worked at a heavy duty class 8 truck manufacturer in their engine development lab, there was a very strong bias among the customer base that a straight 6 was more reliable than a V8. This was contrary to all the field testing, warranty data, etc. I think these biases may have had some truth to them back in the dawn of internal combustion. Once something like that gets ingrained in popular culture, it lasts for generations.

The only grain of truth I'm aware of is that straight 6 cranks are comparatively long and whippy and therefore limit the maximum safe RPM. So if the engines are built for optimum performance at lower crankshaft speeds they may be somewhat less prone to some of the wear and tear that happens to higher speed engines. There have been a few straight 6's with the power take off in the middle of the crank to get around this problem, turning them into two triples in effect. I think the Honda CBX did that but I haven't taken the time to google it to be sure.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

(OP)
"The Chrysler Pentastar 3.6 V6 in my van makes three times the power of an emission-strangled 225 Slant Six (displacement is almost the same) and meets emission standards that the old engine never could and uses less fuel than the old engine, and it weighs less, and it fits transversely which means the vehicle as a whole can weigh less, AND there is a fair chance that it will last longer with less fuss along the way. (So far, so good.) Sure, it's more complicated. But it's built to better tolerances and with better materials. It's got nothing to do with the cylinders being in a V or in a straight line. Technology has come a long way."

This isn't a discussion of old vs new because that is something different entirely. To compare apples to apples you'd have to find an engine of the same vintage. Every engine back then had significantly less power than modern engines. For the most part there was a pretty direct correlation between displacement and power. The slant 6 was one of 6 engines that made it into late 60s mopar muscle car line. Looking at cars that are 50 years old now there are plenty out there where the original slant 6 hasn't been touched and that is very hard to find with an original V8 and to this day have a reputation for being very reliable. Plus the longevity of an engine doesn't really come into question all that often with modern engines. In older cars when the engine went bad that was usually a sign to replace it. Now days when it's time to replace your car it's usually because it's just too expensive to all the little stuff that starts to go wrong. So it's hard to compare the longevity of any modern engine.

When I worked at a heavy duty class 8 truck manufacturer in their engine development lab, there was a very strong bias among the customer base that a straight 6 was more reliable than a V8. This was contrary to all the field testing, warranty data, etc. I think these biases may have had some truth to them back in the dawn of internal combustion. Once something like that gets ingrained in popular culture, it lasts for generations.

Interesting point, I'm guessing perception and bias has some to do with it. But then perception and ease to maintain can go a long way. I'm sure as you know field testing and warranty data can be helpful in showing signs but can't tell the whole story. I take it as something pretty accurate for what happens under 60,000 miles. After 60k miles that kind of data starts to be less accurate. I do think lower RPM, less power, and generally being ran less hard has something to do with it. But there are a lot of examples of high performance straight 6 engines (supra, BMW, skyline, Australian fords) that are well know for how well they hold up in high performance applications.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

#### Quote (eouedu)

Looking at cars that are 50 years old now there are plenty out there where the original slant 6 hasn't been touched and that is very hard to find with an original V8

It is true that there are a lot more original slant sixes out there than V8s- because they sold a LOT more slant sixes than they did V8s.

The reliability of the slant sixes is not present simply because they are slant sixes- there are other factors.

No one with a clue would ever argue that the venerable small block Chevy V8 was 'unreliable'. Architecture is not the reliability-defining variable.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

If I were to put money on which has the better statistical L10 life in normal average use, between a 225 Slant Six and a 3.6 Pentastar, which are both 6 cylinder engines of almost the same displacement but one an old in-line design and one a new V6 design, I'd put that money on the Pentastar. Not because it's a V6 but because it's a modern design with better materials and better tolerances.

If I were to put money on which has the better L10 life between a modern BMW inline six and the Chrysler Pentastar V6, I'd put that money on the Pentastar, simply because BMW. (I've owned German cars.) It's not that it's V versus inline.

It's not the V versus in-line that makes the difference. It's everything else.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

(OP)
If I were to put money on which has the better statistical L10 life in normal average use, between a 225 Slant Six and a 3.6 Pentastar, which are both 6 cylinder engines of almost the same displacement but one an old in-line design and one a new V6 design, I'd put that money on the Pentastar. Not because it's a V6 but because it's a modern design with better materials and better tolerances.

Well again this isn't about old vs. new and I'm not sure why you think you need to make the same point you made before. This was a discussion I am trying to avoid. If you would like to discuss this in a separate post feel free but I don't believe this discussion is relevant to this post.

It is true that there are a lot more original slant sixes out there than V8s- because they sold a LOT more slant sixes than they did V8s.

I guess at this point we are both just guessing. It would be something that is pretty hard to track from either direction. How many are sold, see how many still exist and subtract what engines weren't swapped out in favor of a V8.

My point of this post was trying to figure out if there is something to a design that makes the nature of an inline six more reliable. I just find it more than coincidence that most inline 6 engines in passenger vehicles have a widely regarded reputation of being extremely reliable. I was trying to put a science to why. A few ideas along with a few point people brought up might be part of the reason why but no smoking gun answer as of yet.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

The nature of your original post, and the nature of the specific examples that you cited, implied some degree of old-versus-new, "they don't make them like they used to".

-Cummins diesel all years but specifically the 89-98 "12 valves" are known to be very reliable (OLD)
-Ford 300 straight 6 (OLD)
-Dodge 225 "slant 6" (OLD)
-Jeep 4.0/4.2 (OLD, replaced first with one of a few V6 designs and now eventually with the Pentastar 3.6)
-BMW inline 6 (Some old, some new)
-Toyota supra inline 6 (OLD)
-HJ60 landcruiser diesel (OLD)

Runners up:
-Toyota fj40 gas straight 6 (OLD)
-Mercedes 300D (inline 5 so doesn't get full credit) (OLD although Mercedes still makes plenty of inline sixes)
-Chevy 250/292 (OLD)

... and yet, you failed to mention any counterexamples, of which I will provide just one: the Buick 231 / 3800 90 degree V6 has a well deserved reputation for being bulletproof.

There's another factor at work in the old-versus-new that was built into your original post. Engines that were designed decades ago for automotive applications were (almost) always designed for longitudinal installation. In the case of a 6 cylinder, this presents no particular issue, as long as the engine compartment is long enough, and it's cheaper to make one cylinder head and machine all the cylinders in a row ... UNLESS ... you are going to run the engine down a V8 machining line (like both Buick and Chevrolet did, and Chrysler later on) and create your V6 by, at least on paper, knocking two cylinders out of an existing V8 engine design. As an aside, the Chrysler pushrod 3.9 V6 that was one of the engines that replaced the Jeep 4.2/4.0 and the 225 slant six, is three-quarters of a 5.2 V8 a.k.a. 318 V8. But nowadays ... Most new engine designs for automotive applications are designed to accommodate transverse installation and that means it's almost sure to be a V6. So ... Inline almost equals old (or heavy truck) with a few exceptions, V almost equals new with a few exceptions.

Now, the second part of your post.

-less powerful so they aren't used as hard (There is absolutely no correlation unless you compare old versus new, or run-of-the-mill lump versus high-performance. And if you hot-rod the engine as you describe, this is out the window anyhow.)
-easier to access and work on therefore they are maintained better. (This is an application / installation issue, not an engine-layout issue. There is no difference in how you change the oil between a chrysler 225 and a buick 231, it's the same process. And the 225 required manual valve clearance adjustments whereas the 231 had hydraulic lifters ...)
-less moving parts (The only difference is in the case of overhead cam having more camshafts and a double set of cam drives. If it's pushrod, it is exactly the same. Also, SOME V6 layouts need a balance shaft to operate smoothly. 60-degree V6 with 60-degree offset journals, the current modern layout, doesn't need one.)
-Power peaks at lower RPMs so it takes less to do more (This is a TUNING issue, not an engine-layout issue. BMW inline sixes can spin pretty fast!)
-less prone to hot spots so less chance of detonation (Why? All else being equal - No difference.)
-being upright gives more lubrication around the cylinder walls because gravity isn't working against the high side of the cylinder wall (Bunk. The gravity forces are trivial compared to the oil being pumped in under pressure and squirted out and thrown around. And in any case ... a Chrysler 225 SLANT Six is tilted over 30 degrees, the cylinder inclination is exactly the same as that of a 60-degree V6! Many BMW sixes are tilted over as well. Same reason - hood clearance.)
-being upright applies the same theory for cooling and every other part where gravity could be fighting a v engine (See above)
-more bearings in the crankshaft (ford 300 has 7 main bearings) (This is the one thing in which the inline configuration can have an advantage. On the other hand, the crankshaft is longer and more prone to torsional vibration. By the way, the Chrysler 225 slant six only has 4 main bearings.)
-better balanced (Really? A 60-degree V6 with 60-degree offset journals - which is the usual modern arrangement - does not need a balance shaft. My Pentastar is a darn smooth-running engine.)
-more surface area exposed to air and more open engine bay for it sheds heat better (This is an application / installation issue, not a cylinder-layout issue. And in any case - in a liquid cooled engine, the heat rejected by convection and radiation from the cylinder block is peanuts compared to that removed by the coolant. And it's easier to get good coolant distribution on a shorter engine, i.e. V6 ...)
-less nooks and cranies for old oil and engine particles to hide when the oil is being changed (Really? Where's the difference?)
-less parts of the engine hidden that aren't as well lubricated and/or cooled (Really? What parts?)
-I don't believe any of the above mentioned engines have timing belts, it's either a chain or gears (again this is application specific and is not pertinent to inline or V ... it can be done either way with either configuration)

The title of this thread implied that, at least in your mind, it was a foregone conclusion that an inline-six was a better layout. I'm picking your post apart because ... I don't think so! There are too many other factors at work.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

(OP)
Thank you all for you input.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

The perfect primary and secondary balance makes them pleasing from an NVH perspective. But that's unrelated to reliability.

Steve

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

I don't put much store in online popularity contests.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

I have heard the Subaru engine called bullet proof and it is neither straight, Vee, nor vertical.
Many Beetle engines outlasted the car.
Engines that have a reputation for early failure generally have a design flaw which is not related to cylinder orientation.
For years the slant six was the petroleum industry standard test engine for fuel additives to combat carburetor icing.
Most lists of the ten best diesel engines list both the six cylinder DT466 and the V8 Duramax.

Bill
--------------------
"Why not the best?"
Jimmy Carter

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

#### Quote (OP)

Ford 300 straight 6...

The Ford "Barra" engine, descended from the above, is highly praised on the various Aussie motoring YouTube channels (such as Mighty Car Mods and Skid Factory).

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

#### Quote (eouedu)

I don't want to start an engine debate but I know enough that generally straight 6 engines have a reputation for being more reliable than a V6 or V8 configuration. Just to simplify this discussion I want to stick with a discussion of older pre efi passenger vehicle and pickups engines because that is what I'm interested in. There aren't that many inline 6 engines out there but most of them have a very good reputation for being reliable.
<snip>
It might be as much a social issue as a mechanical one.

Whatever truths may be contained in the original post is probably more a consequence of the kind of drivers who bought them, tending (as a group) to drive more mildly than those who bought more powerful engines. IOW, it wasn't the IL-6 configuration that gave rise to reputations for reliability so much as it was in the nature of most people who chose them to drive more gently. 60 years ago, people were less inclined to buy more than what met their needs; these people had lived through the Great Depression of the 1930's and WWII, and frugal attitudes were far more prevalent as a result.

Norm

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

If you limit the discussion to the classic inline six vs v6/v8 without efi, then we are talking about rather old designs with a rather limited power output designed in a era where the knowledge of construction materials was limited, calculation was essentially done by sliderule and manufacturing precision still was rather crude. That design method resulted in several designs, some in hindsight rather good, others not so.

On the basis of what were some engines better then other? Maybe to a certain extend by design - but some most likely where engineered better by sheer luck without the designer knowing it at that time. Compared with modern design and production, those "classic" engines were developed and produced on the basis of "hit and miss" and some performed remarkably well.

But none of them comes even close to modern designs that are well designed and produced to very tight specs delivering a lot more power over a longer time with less fuel and emissions with much larger maintenance intervals.

I think it is not really possible to rate the ancient engines in terms of reliability (whatever definition you use for it) because of the lack of reliable data. What we "see" as reliable most times is based on anecdotal evidence that subsequently is accepted by a large number of people - but not backed up statistical data.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

#### Quote (VE1BLL)

The Ford "Barra" engine, descended from the above, is highly praised on the various Aussie motoring YouTube channels (such as Mighty Car Mods and Skid Factory).

Thumbs up to MCM and TurboYoda.. One test of the strength of original designs especially the bottom end, block rigidity, choice of internals e.g forged crank, beefy rods, closed deck for which the 2JZ is a legend and also the Barra (after beefing up the valve train and head bolts) is the degree of turbocharged boost the engine can be take stay in one piece.

A raw 2JZ block looks more like a casting for heavy duty diesel application than automotive gas engine applicaiton.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

Another thing that really helps engines of the modern era rack up the miles without overhaul is good crankcase ventilation, along with low blow by (cylinder stability and finish, piston ring technology, valve stem sealing, and probably a bunch more) and accurate fuel delivery (Fuel injection and engine management).

As "proof" when the EOM gets PCV wrong, the other two aren't enough by themselves. Witness Toyota, Mopar, Audi, VW, etc sludging.
https://www.consumerreports.org/cro/cars/car-parts...

Then again, if cooling system maintenance is neglected for 60 kmiles or so, radiator and rotted head gasket issues can kill an engine right quick. Just like the olden days.
As can a simple radiator cap that doesn't hold pressure if the engine design or operating conditions permits localized hot spots that spawn severe nucleate boiling and resulting cracked heads. Whee.

Some manufacturers are consistently WAY better at all this than others, making the statement that all manufactured products are designed to just survive the warrantee period ring pretty hollow.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

If a person searches forums and engine failure sites you will see there are plenty of modern designed and manufactured engines that don't come close to the longevity of the old stuff. Then there are the cases of massive sludging problems that were occurring even with proper oil changes. IMO any reliability problems are not from the cylinder arrangement, but the materials and the design as well as how well the engine design is matched to the application and what percent of the power that the engine is capable of is used during its life as well as the rpm range it runs in, oh and then who does the manufacturing as well. A normal driven Geo Metro 1 liter will last for years, as will a 1UZFE both can go over 300K miles easy with a bit of normal maintenance, and neither one is a overly fabulous design.
I saw the mention of Pentastar, they had a huge rash of birthing problems with the goofy integral exhaust manifold in the head that didn't help with valve seat retention, this is from memory it has been awhile since studying that one. I did just watch a video of one that had a roller follower failure on a 2018 3.6 with 4,000 miles so?

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

From Tmoose's link above: Used-car shoppers should also realize that even the most complained-about engines represented less than 1 percent of those made, so the odds of avoiding such a car are in your favor.

So to me, when 99% of the engines don't have the problem, it is not a design issue. There has to be some other contributing factor(s). Either poor quality control, poor maintenance, unusual environmental conditions, something other that a design flaw or more would have the problem.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

My 2004 6 liter Powerstroke started started having problems at 50K miles. It was hauled away this last weekend with 140K on it. I bought a diesel truck because of their reputation for durability. It used to be you could run diesels on used motor oil. They are now made to such high tolerances that a tiny piece of grit can cause a cascade of failures that disables or destroys the engine. The 6 liter used 20 quarts of oil, which also operated the fuel injectors so oil cleanliness was essential. It had 10 micron and 5 micron fuel filters in series. It used a special grade of coolant that was expensive and hard to find. All maintenance and repairs were expensive. I spent $4000 replacing the oil cooler and EGR cooler with an after market "Bulletproof Diesel" kit, when these went bad. These were well know problems after the engine was out a few years. I bought a gas truck to replace it. At the time, I read that diesels were a$5,000 option compared to gas engines, but when looking at prices on the market it seemed more like $15,000. My experience with Ford dealer service in my area was horrible. ### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration? Hailing from the days of the 'shade-tree mechanic" and the 'points-plugs-condenser' routine - your REALLY motorhead buddy owned a timing light - and fifteen thousand miles on a set of bias-ply tires, I don't want to roll back the clock, not ONE bit. old field guy ### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration? I think I still have a timing light somewhere. ---------------------------------------- The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows. ### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration? My old Acura TL is still running strong with 240,000 miles on its 3.5L V6. I never had even a minor problem with it. I loved it so much, I bought the 2017 Honda Accord with the same engine precisely *because* it had the same engine. Sadly, Honda/Acura dropped the engine from passenger cars in favor of turbo fours in 2018. As for old versus new, I sure don't miss cleaning and gapping plugs and points, adjusting valve lash, and replacing clutches, but I do miss how they helped build a *relationship* with my cars. My 30 something nephew (who once raced sprint cars) got in my 1993 RX-7 the other day and said "I miss these old school cars. They've got soul." I think he's right. New cars are certainly "better" but I feel no connection with them. ### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration? Well for a real comparison, does anyone have reliability statistics on a Detroit Diesel 2-71, 3-71, 4-71 and 6-71 versus a Detroit Diesel 6V-71, 8V-71, 12V-71 and a 16V-71? Bill -------------------- "Why not the best?" Jimmy Carter ### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration? Experiences will differ. Many drivers would toodle around gently, never mashing the accelerator pedal to the floor and never exploring the rev limiter. 'Reliable' in such a light duty context is merely an indication that the engine doesn't have any serious design or build errors. Other drivers would be full throttle and at the red line several times just going to work in the morning. 'Reliable' in the severe duty / abuse context is much more illuminating. By way of example, when I was young I owned a Dodge Dart with the 225 Slant-6 engine. I recently learned that the Slant-6 red line was supposed to be 4500 rpm. Oh dear. I recall assuming at the time it was 6000 rpm, and treating it as such. For years... 'Reliable' ### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration? A straight 6 engine not discussed here is the Volvo B30 engine which started life as a carb engine and in its last iterations before it was dropped in favor of a V6 was EFI. The engine had a reputation for reliability and would regularly run 200,000 miles before overhaul. It is also interesting that the V6 that replaced that engine was a terrible engine, prone to head leaks and camshaft failures. B.E. You are judged not by what you know, but by what you can do. ### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration? Before somebody comes back and mentions it, I know the B30 was prone to crankshaft failures when people tried to soup it up, because of torsional resonance in that long crankshaft. B.E. You are judged not by what you know, but by what you can do. ### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration? The V6 that replaced the B30 inline was the PRV. I don't think it's crappiness had anything to do with its cylinder arrangement. It was simply a crappy design. ### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration? I used to look through CANBUS data for real customers. In something like 7 million minutes of operation nobody exceeded 5000 rpm. Obviously my car didn't have a recorder on it! I was actually looking for the distribution of real life braking accelerations, that was interesting and useful. Cheers Greg Locock New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? ### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration? Anyone who thinks straight sixes are magically reliable and that Subarus are reliable hasn't been around many automotive machine shops. Most of the old iron straight sixes mentioned were somewhat reliable because they didn't make enough power to hurt themselves. Every job shop gets a steady flow of Subaru cylinder heads. They blow the gasket, warp the head. The local repair shop has learned how to pull both heads, bring them in, we mill them without removing the valves, pressure test, out the door and back on the car in the same day. As far as the original VW air cooled engines outlasting the car, I've personally never seen it happen, but then I didn't live in the rust belt in the VW heyday. Maybe if the body rusted out really quickly. However, it was another engine designed unable to make enough horsepower to hurt itself. If the oil cooler was kept clean and the oil changed regularly and the valves kept adjusted, they would run a while. But like the Subaru, it was possible to swap a VW engine in the driveway in an afternoon. #### Quote: My 2004 6 liter Powerstroke started started having problems at 50K miles. It was hauled away this last weekend with 140K on it. I bought a diesel truck because of their reputation for durability. It used to be you could run diesels on used motor oil. They are now made to such high tolerances that a tiny piece of grit can cause a cascade of failures that disables or destroys the engine. The 6 liter used 20 quarts of oil, which also operated the fuel injectors so oil cleanliness was essential. It had 10 micron and 5 micron fuel filters in series. It used a special grade of coolant that was expensive and hard to find. All maintenance and repairs were expensive. I spent$4000 replacing the oil cooler and EGR cooler with an after market "Bulletproof Diesel" kit, when these went bad. These were well know problems after the engine was out a few years.
FWIW, there is some truth to the above. Yes, Ford had some issues with the 6.0., but a '04 gas truck worked as hard as a 6.0 can work would have been dead years ago. Yes, the 6.0 EGR system is simply a flawed design; pumping corrosive exhaust gases through a thin radiator shared with the engine coolant was inexcusable. They all failed; some sooner, some later. When they do, it blows out all the coolant and put the truck out of service instead of just needing service when convenient. I've replaced the EGR cooler one time and am still driving my '04 6.0 every day with 185,000 on it. No, the coolant isn't especially expensive or difficult to find. Good fuel filters are a good thing. Lots of oil capacity in a heavy duty truck is a good thing. The 6.0 has the easiest to service fuel, oil and transmission filters I've ever encountered in sixty years of doing maintenance. You forgot to mention the variable vane turbocharger will rust up if not driven hard and regularly.

When the 6.0 began having teething problems, some looked back fondly on the more reliable 7.3 it replaced; yet another example of an engine being reliable because it didn't make enough horsepower to hurt itself; more iron than output. The 6.0 made fifty more horsepower with better fuel economy and met emissions requirements.

jack vines

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

Jack, you must be talking of the VW air-cooled engines. Those were from an era where 60,000 miles was considered normal service life. (So, for that matter, are quite a number of the engines that have come up for discussion in this thread.)

From the water-cooled era - The VW "2.slow" - 2 litre 4 cylinder 8-valve iron block - is another engine that doesn't make enough power to hurt itself. VW managed to screw some of them up by installing some piston rings upside down, which made them oil-burners, but otherwise they didn't break. Even if the timing belt was neglected and broke, at least the early 8-valve engines were non-interference. Unfortunately, that engine offered neither power nor gas mileage, and so it's not on the menu any more.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

#### Quote:

Jack, you must be talking of the VW air-cooled engines. Those were from an era where 60,000 miles was considered normal service life. (So, for that matter, are quite a number of the engines that have come up for discussion in this thread.)

From the water-cooled era - The VW "2.slow" - 2 litre 4 cylinder 8-valve iron block - is another engine that doesn't make enough power to hurt itself. VW managed to screw some of them up by installing some piston rings upside down, which made them oil-burners, but otherwise they didn't break. Even if the timing belt was neglected and broke, at least the early 8-valve engines were non-interference. Unfortunately, that engine offered neither power nor gas mileage, and so it's not on the menu any more.

For true, Brian. I edited my first post to clarify that point. For those of us old enough to remember when they first arrived, "VW" has only the one referent. The more recent fifty years are muddied up with Audi, Porsche, SEAT, Bentley, Bugatti, Lamborghini, Ducati, Skoda, et al.

jack vines

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

PackardV8, my experience when an Al head with OHC warps, well that warp happens after the fasteners are removed and then the cam or cams won't turn. If they are machined flat in that released state then when re fastened wouldn't the cams be locked from the bores still being warped or misaligned? Just curious how that all worked out.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

This started as a comparison of straight 6's versus V 6's and V 8's.
Possibly the best comparison is the Detroit 71 series and the Detroit 71 series.
A lot of the same parts are used in the straight 2 cylinder, 3 cylinder, 4 cylinder and 6 cylinder engine as are used in the V6, V8, V12 and V16.
Many of these engines share the same pistons, liners, heads, valves, blowers, con rods and a lot of other parts.
I have never heard any comments or anecdotes regarding the reliability of straight 71 series versus the V 71 series.
What experience have others had with the comparable reliability of these engines.
Surely this is one of the best example of apples to apples that we will find.
Any comments and/or first hand experience?

Bill
--------------------
"Why not the best?"
Jimmy Carter

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

Well if you want to talk Detroit Diesel... Once upon a time, many moons ago, when men were men and giants walked the face of the earth, I worked at Detroit Diesel as an engineer in the warranty investigation department, where our job was to determine root cause of failures.

I worked on major warranty campaigns across several platforms, including Series 71, 40E, 6.2 and 6.5 liter, eventually Series 60 and then very early development work on DDXX engines, and even some ancient 110s at one time.

I never worked on a campaign on a production platform where a major component failure was the result of component design shortcomings related to engine configuration.

The Series 71 especially is a platform where a large number of configurations are possible from a relatively small number of individual parts; V engines use heads from smaller inline engines (Series 71 V16, for example, uses cylinders/liners from every other Series 71, along with 4 Series 71 inline 4 cylinder heads).

The vast and overwhelming majority of problems with these engines are the result of controls problems. Frozen pumps/injectors, failed sensors, emissions gear, etc etc. I can honestly say that across dozens of campaigns across these platforms, all of which were successfully solved for either single cases or engineered changes to a design, there was not one case where a problem was tied directly to architecture.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

Well, that just goes to show, at least, that the designers of the 71 series knew how do design a Vee engine as well as an inline engine.
Such as they are, I guess the balancing challenges for a 2-stroke engine are generally less than a 4-stroke engine.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

An inline-four 4-stroke wants to have the two inner pistons moving together and the two outer pistons moving 180 degrees opposite to have an even firing order. An inline-four 2-stroke wants a crossplane crankshaft (90-degree firing intervals). An inline-six 4-stroke has a symmetrical crankshaft front to rear (two
mirror-image groups of 120-degree spaced crank throws) to have an even firing order and is almost vibration-free. An inline-six 2-stroke wants cylinders firing 60 degrees apart to have an even firing order. No two cylinders will hit TDC at the same time.

A google search of a picture of a 4-53 crankshaft suggests that it is a crossplane (90-degree firing intervals). A google search of a 6-71 crankshaft suggests that the front group of three has crank throws 180-degrees opposite the rear group of three with cylinders 3 and 4 180 degrees apart, cylinders 2 and 5 180 degrees apart and 120 degrees offset from the inner pair, and cylinders 1 and 6 180 degrees apart and 120 degrees offset from the others.

I know the inline-four crossplane-crank configuration requires a crankshaft-speed opposite-direction balance shaft ... see 2009-on Yamaha R1. I don't know if the Detroits spun fast enough for it to matter.

A google search of a 6V53 indicates that it has a 60-degree bank angle with common crankpins for the corresponding cylinders in the left and right bank and there is a big counterweight on each end of the crank outboard of the outer main journals.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

Quick thoughts....

Inline 6 has nice balance...
v6 and v8s have timing belts/chains a mile long plus lots of extra spinning stuff to cater for said mile.

I own an E39 inline 6 for the past 7yrs....spent most of that time at or near redline - driven very hard, always. Engine has never been opened, not even once for anything in that time so that makes me biased right away!

Bar a v12, the inline 6 is perfection in my opinion.

Brian,

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

Add a turbo, and it just gets better... near ideal 240 degree phasing between exhaust pulses, if the designer troubles to split the manifold in half front to back, and spec a twin entry turbine housing.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

Why must V6 and V8 engines have mile long timing chains and 4 cams???

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

@ Lionel,

I was moreso talking about the European ones...I guess there are Us hemis and such with pushrods and 2 valves, but we dont really count those in Europe and they are considered prehistoric in terms of design...

Brian,

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

Yes, God forbid an engine has pushrods. Don't worry about the fact that they actually do work fine for moving a valve.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

"Work" yes, but it's harder to do independent valve timing for intake and exhaust, and it's harder to do 4 valves per cylinder. If you want good emissions, and good fuel economy, and good power, and fit the engine transversely, and not approach 90/10 weight distribution, DOHC is the way to go (and there was another thread some time ago discussing this).

But this is scarcely relevant to the inline-6 versus V-configuration argument, since there have been both successful and unsuccessful combinations of every practical cylinder and valvetrain configuration. My van has a Chrysler 3.6 Pentastar in it, which is DOHC 4-valve with independent VVT on intake and exhaust, complete with the chain drives getting to the top of the engine. It has been good for me, and if there is any rampant issue with cam drives on those engines, I'm not aware of it. That engine replaced several other V6 and V8 engines in Chrysler's lineup, which were various pushrod and SOHC designs. The Pentastar has more power, better emissions, and is more efficient than any of the engines it replaced.

Still ... irrelevant to the inline-vs-V discussion. The Pentastar fits transversely under the hood of that van. The old inline slant 6 would not!

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

Talk of complicated V8 DOHC schemes making the V8 less reliable doesn't have any relevance when comparing V8's against those old I6 engines.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

Good thing I don't want transverse engines. Please don't tell my C6 Corvette it doesn't have good emissions, fuel economy and power. Just try to package a DOHC under that hood.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

Nice car ... and it has a highly developed engine, pushrods and all. I sure wouldn't suggest replacing that engine with an inline six, either

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

Agree with Lionel, no savings at all with overly complicated valve actuation systems, when very expensive failures occur at very low mileage. And dare not have the correct paper work to prove oil changes, then you can be stuck with the 60K replacement cost of an engine, depending on the manufacture of course. Just my opinion.

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

#### Quote:

I own an E39 inline 6 for the past 7yrs....spent most of that time at or near redline - driven very hard, always. Engine has never been opened, not even once for anything in that time so that makes me biased right away! Bar a v12, the inline 6 is perfection in my opinion.

No one example proves the rule. I have a neighbor who spits on the ground and curses when BMW is mentioned. He thought he was buying prestige and instead his E39-engined Bimmer bought endless trips to the dealer service department for major and minor fixes. Over the two years he owned it, it was in the shop more than he drove it and finally got out from under via the lemon law, but only after ugly hassles involving lawyers. It was his worst car in forty years of ownership.

Another poster here hates his IH V8 diesel and claims they're junk. A friend in Alabama who owns a fleet of rollback car haulers laments that he can no longer buy trucks with that engine. He says with regular maintenance, they ran forever; his most reliable engines in forty years in of medium duty trucking.

jack vines

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

#### Quote (Packard)

He says with regular maintenance, they ran forever; his most reliable engines in forty years in of medium duty trucking.
That would be the 7.3 that you cite as an example in a discussion of the 6.4
Different engines, different stories.
IH has made more than one V8. Some are better than others.
The recommended oil change interval for the Maxxforce 7 (6.4L) is 15,000 miles. The IH service manager told me that one customer is changing oil in his Maxxforce 7s every 3,000 to 5,000 miles.
It's a good thing that there are lots of dog lovers out there cause this engine is a dog.
At the moment it is still running well and has less than 50,000 miles.
Anyone who thinks that it is getting a bum rap is welcome to buy it.

Bill
--------------------
"Why not the best?"
Jimmy Carter

### RE: What makes an inline 6 engine more reliable than a V6 or V8 configuration?

#### Quote:

instead his E39-engined Bimmer bought endless trips to the dealer service department for major and minor fixes.

E39 is a chassis code, not an engine code- E39 is the 95-'03 5 series which came with many different engines.

The BMW I6 is known to be relatively reliable, with a few exceptions (water pumps with plastic impellers, noisy variable valve timing gear). The V8 in the 540 is bombproof, the V8 in the M5 less so... the I4 was a dog and did not requite itself well.

So there's a myriad of possibilities for someone to have a bad experience with an E39.

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