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RPM on cold engine?

RPM on cold engine?

RPM on cold engine?

(OP)
Hello there,

I am very new to this forum, and I gotta say, it was a bit confusing to get to this point ;)

Anyway, I have been thinking a bit lately, and I hope that you guys can help me.

You see, constantly I get told that when my engine is cold, I have to run on low RPM's, however, I do not completely agree to that.

Now my engine is quite strong, so it doesn't have much trouble on the low RPM's too, but heres my idea of how it should be:

My father, who works for ZF (transmissions) says that a cold engine should never run more than 2k RPM, the same thing I am told from both my sister and her boyfriend, who both have an education in the area. Still, I do not really agree.

My point of view in this matter is that an engine should never "laboring" (that's what google translate told me, I have no idea what the word is in English). What i mean, is when an engine is having trouble to pull itself and the car at very low RPM's, I'm sure you know what I mean.

Anyway, my engine has a bit trouble at those low RPM's, it is a straight 6 with 200HP, and even though it has Vanos (yeah, BMW) it is still quite slow at those low RPM's.

Back to the question: What are the appropriate RPM I should run my engine on when it is cold? I normally just change gear when I hit 3k RPM, but almost everyone is nagging me about doing so, "It is not good for the engine" they say.

The car is a BMW 525 E34 with a BMW 2.8 M50B28 engine which very few modifications to it. The intake manifold has been ported a bit bigger, and it has a bigger exhaust manifold, yet the rest of the exhaust is stock.

Thank you for reading my novel :D

RE: RPM on cold engine?

Are you an engineer.

What does the owners manual say to do.

The best procedure varies with different engines but basically when reving a cold engine to high, you have to high oil pressure which strains the oil pump drive. You also have poor oil circulation and you have excessive clearances between some engine parts until thermal expansion reduces the clearance when the engine is at normal operating temperature

Regards
Pat
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RE: RPM on cold engine?

Common sense should dictate not to overrev a cold engine, but to drive conservatively for the first few minutes.  Here, let's differentiate between a 'cold' engine in very Northern latitudes and those of 'cold' engines in, say LA or Sydney.  

I personally see no problem with 3000 in your particular BMW but have never seen anything in a manual.  I have seen the 3000 rpm "do not exceed" in the specs from Cosworth for the "care and feeding" of their oil pump (racing application).

Rod

RE: RPM on cold engine?

I once crossed paths with an engineer that had worked on hydraulic lash adjusters earlier in his career.  He related stories about worst case test scenarios for lash adjuster "pump-up".  This involved cold soaking in a test cell to -40deg, followed by startup & WOT operation to whatever rpm the engine could sustain.  A successful outcome was where adjuster pump-up did not occur, and the engine either settled into a non-pump-up-limited rpm, or a catastrophic bottom end failure pre-empted any pump-up issues.
While you may shorten your engine's life via revving it through gears when cold, I doubt you'll ever know the difference.

RE: RPM on cold engine?

hemi

That is unless he breaks something in the oil pump drive or blows a filter canister. I have seen both happen albeit on modified engines running racing oil.

I have also seen pressure relief valves occasionally stick which could also result in dangerously high oil pressure when cold.

It can also on occasions crack a skirt on a piston, but once again unlikely.

It certainly puts more load on the rings and valve train before they are fully lubricated.

Taxi cab engines normally last 2 to 3 times longer than the identical engine in a grocery getter. Partly because the miles occur over a much shorter time frame, but also because of greatly reduced cold starts. As to whether or not the difference is enough to matter while the current owner has the car is of course a valid argument.

OP

As to an arbitrary one size fits all answer, some big diesels won't even reach 3000 rpm. Some race engines idle at 2000rpm or more. Many modern engines now have precision made hypereutectic alloy cast pistons with Teflon coatings on the skirt that even cold only have 0.0005 to 0.001" piston to bore. Some high performance supercharged engines have high strength alloy forged pistons with maybe 0.006" or more clearance when cold. Like Rod says, it really does depend. RTFM. It was written by engineers that actually know what is in that model engine and have done extensive testing.

 

Regards
Pat
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RE: RPM on cold engine?

''my engine has a bit trouble at those low RPM's''

Yes, but in what gear?

Its not going to labour in 1st at those rpms...

Ive got the 525i e39 (m54 engine), which is twin vanos, once I see the temperature gauge hit 1/4 way up I give it socks.

Ive done this on 16 of my past cars, Gtis, Bmws, Audis, Porkers, etc.
Ive also stripped them all down at one time or another to rebuild for more power. Ive never seen anything odd in there which tells me there is nothing wrong with nailing it at this point.

Given that all the performance Bmws have an rpm limit when stone cold at approx 4000rpm, which increases as the temperature rises, it further enforces that this practice is fine. Im sure they tested it real good, especially on the m5s.

Once my engine is hot, and Im on a nice piece of road, it never sees below 4500rpm, the inline 6(and bigger) engines and gearing are designed to function at their best above these rpms. They do like petrol above that, but its worth it.

If your still uneasy, fit an oil temperature and pressure gauge and pick a ''target nail it figure'' that makes you happy.
The pressure will drop as bearing clearances open up, and then level off.
If you're fitting a mechanical oil pressure gauge, do not use a copper line into dash. They still supply copper with some gauges.
Copper work hardens with vibration and can lead to many problems.
From filling your radio with hot oil, to deep frying your knees, or causing a very large engine fire.
So use nylon tube.

Since you have an iron block, the heat transfer through the metal from coolant jackets, and passageways, etc to oil passageways wont be as ''fast'' as if you had an Aluminium block. So...you could also add an oil/coolant heat exchanger device to increase the rate of heat transfer, from the coolant to the oil.
This will have two benefits.
It will heat the oil faster after startup, since the water gets to temperature before the oil.
When you're up to temperature, and driving it hard, it will then act as an oil cooler.
If you're buying one, and want the best one, get a Laminova.
You will need some form of oil tap off plate mounted under oil filter assembly for the flow and returns though.

Having said ALL of that, I wouldnt worry about it, unless its keeping you awake at night.

Wait until needle is 1/4 way up, and off you go...

Brian,
 

 

RE: RPM on cold engine?

So the question I have to ask, what are you calling cold?
How many minutes of run time?
In the end you don't have to listen to any advice, its your car / engine run it how you wish. If it was an aircraft engine you would likely want to follow proper warm up, because falling out of the sky would be one option for not doing so, and of course the resultant hard impact with the ground.

RE: RPM on cold engine?

(OP)
Patprimmer:
I am no engineer, yet I know a few stuff about these things.

The manual didn't really strike my mind. I did look at it in my old car, Ford Sierra 2.8 V6, but it didn't say anything about cold start. I do not have the manual for my BMW. An option would have been to find it on the internet, I don't really know why I didn't look for it.

Evelrod:
That is indeed common sense. I was just curious as to where the barrier were. My car is no racing car, but I do not lack on the oil, it gets the best I can find. But I really have no idea if it acts differently than what you would use on a "grocery car". I use mine as an every-day car.

Patprimmer (again):
I get that is does indeed differ from car to car, which is why I put my engine specs in my first post, so that I could get a more accurate answer.

Briangar:
In first gear it does not have trouble, but when I hit third or fourth it can indeed have a bit trouble when it gets under 2k RPM, and I would say that it starts to labour down there, and if I need to go like 90 km/h, which I do about half a minute after the car is started, then it will have a bit trouble down there.

Hemi:
That I did not expect. I am constantly getting these horror stories from my families and friends about people who rev's the engine above the 2k RPM mark, as I said in my first post, I was a bit skeptic about that.

Patprimmer:
I was unaware that it could affect the oil pump. I do not have a pressure gauge or temperature gauge for the oil, so I really don't know what's going on with the oil. I was actually more worried about the pistons, since they won't have expanded fully when the engine is cold.

Briangar:
You answer certainly cleared things up for me. Are you sure that the M50B28 engine is an iron block? It really looks to be aluminum. Maybe it's just the headers and the Vanos thing which is.
Thing is, the temperature gauge goes up to middle VERY fast, and then it stays there - rock solid. It doesn't even take it more than 2 minutes before the engine is hot, and I can heat the inside of the car. I asked a few people about this, and they said that I should trust it, but when heat comes to the windscreen and the inside, then water has to be hot, which means that the engine is hot. How long does it take for your engine to get hot?

Dicer:
I apologize for not clearing up what I call "cold". I live in Denmark, and the winters can be pretty rough. This winter we didn't get under the 0 degrees much, but it happens. Last winter we had -15 degrees Celsius.
I know that I do not have to take any advice, but in my 21 years of living, I have found out that some advices are good to follow, if they make sense and a proper explanation is given.

The past posts has really enlighten me, thank you.  

RE: RPM on cold engine?

Denmark - alloy block then. Us got Iron.
It takes mine approx 1 mile to get to 1/4 hot. If you take it easy from then on, about two more miles to get fully warm - half way up.

I do believe the m54 engine is far more thermally efficient than the ones before it, and concentrate more energy into moving the piston, and less into the coolant.

2 mins to interior heat is pretty short, but its an old(ish) engine.

Some of the new Lexus 'I believe' have either electric heaters in the cabin, or in the coolant lines to heater matrix as the engine is so thermally efficient it needs a booster for interior heat on cold mornings.  Take note, I didnt see this with my own eyes, nor read it, but was told it a while back, so may not be true!

Im not at all familiar with the fancy Toyota's.

Brian,

RE: RPM on cold engine?

Factory temperature gauges are not true thermometers in that their scale is far from linear. The basically say, cold and thermostat not open, thermostat open and running in desirable controlled range and very hot, with a long dwell but a quick transition.

It is important that the oil is also reasonably warm. This depends somewhat on the grade of the oil.

 

Regards
Pat
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RE: RPM on cold engine?

(OP)
BrianGar:
I have heard of those electric heaters too, so there must be something about it. I just don't believe that mine has such one, the car itself is from 1990, and it doesn't heat fully up before the temperature gauge is at half, but it really heat up fast, which I am very amazed of. I can count it on being hot enough inside the engine itself once it starts heating, right?

Patprimmer:
The oil that I am using is Shell Helix Ultra Racing: http://www.shell.com/home/content/products_services/on_the_road/oils_lubricants/cars/find_right_car_oils/helix_ultra/ultra_racing/

If I use a cheaper oil, my valves on the headers starts to tick, like they do when I start the engine at first, before it can make pressure for the hydraulics, which brings me to another minor question.
When I really push my engine by going sideways, it often starts to tick in the valves pretty quick, no matter what oil I use. I cannot imagine that it is good for the engine, and I am told that it shouldn't happen. I bet it can be pretty much anything, but when it only happens when the engine is working hard at high rev's (I never do this on a cold engine) may tell a bit about what it can be?

RE: RPM on cold engine?

We were an engine component supplier to BMW in the 80's & 90's and used to accompany them on cold start tests in Finland.  Their test methodology was to let the vehicle cold soak overnight outdoors, the colder the better.  -30C was common, sometimes colder.  Then they started the engine and drove away immediately at full throttle, shifting at redline.  Never saw any damage done.  I still would not do it to my engine.  A couple miles of driving gently is the best way to warm up an engine.  If I had to get to high speed within a 1/2 mile I would let it idle a few minutes first.

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

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: RPM on cold engine?

Start it up, put some load on, give it beans when you feel the heaters working.

- Steve
 

RE: RPM on cold engine?

(OP)
dgallup:
Thank you. That is what I needed to hear. I bet that it won't take any damage running with a bit higher RPM than what I am constantly hearing from friends a family.

SomptingGuy:
Pretty amazing if the engine itself it hot enough after just two minutes. I think I'll stick with 3 - 3,5K RPM until it is fully heated.

RE: RPM on cold engine?

heaters working = thermostat open = nice warm engine

- Steve
 

RE: RPM on cold engine?

Quote:

heaters working = thermostat open

No it doesn't.

RE: RPM on cold engine?

Can't argue with your <<no argument>>

It is, you know!

- Steve
 

RE: RPM on cold engine?

Quote:

In first gear it does not have trouble, but when I hit third or fourth it can indeed have a bit trouble when it gets under 2k RPM, and I would say that it starts to labour down there, and if I need to go like 90 km/h, which I do about half a minute after the car is started, then it will have a bit trouble down there.

Gee, I would have never figured that out.  Oh, by the way, that's what the shift lever is for. Common sense dictates a lower gear when an engine "labors", hot or cold.  90kph at under 2000 and in top gear would indicate cruise with a light throttle (or a parade)...wiggle that lever on the floor a bit and your problems will go away.

Rod
 

RE: RPM on cold engine?

SomptingGuy, the thermostat blocks coolant flow to the radiator until the coolant is warm enough to open the thermostat. Coolant to the heater core does not flow through the thermostat. It simply recirculates through the engine block.

RE: RPM on cold engine?

What's a M50B28? Never heard of that one.
You write 525 E34, do you mean M50B25TU (the updated version with VANOS)?

Anyway, recommending below 2k rpm for an engine that redlines at 6500 is ridiculous. And the M50s were always weak at low rpms. Run it up to 3500 before shifting when it's cold, that will work fine for you.

I have a feeling that your family drives Diesels...

Cheers,

Benta (who drives his 4th BMW straight-6 without any problems...)
 

RE: RPM on cold engine?

I'm pretty sure that heater hoses are on the engine side of the thermostat, at least in British cars.

I once tried to persuade the chief engineer on this

http://www.youtube.com/watch?v=UQuzHU3JVWU

(the first car ever to use a part designed by me!) that cold passengers were less important than a warm engine, but he ignored me.

 

Cheers

Greg Locock


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RE: RPM on cold engine?

Steve.

On my 1989 model Honda Integra, the heater core is plumbed into a thermostat bypass line. It akes water from the head before the thermostat and feeds back into the pump suction side of the thermostat housing. I just looked to check to make sure. That is the logical way to get the heater/demister to clear the screen in minimum time although it does increase engine warm up time. Also the Honda does have a cold start "tune" in the ECU and is sluggish and limited to probably about 4000rpm until the ECU decides it's warm enough. I only know because of the rare occasions where I had to pull directly onto a freeway from a dead cold start and getting up to speed was more on my mind than preserving the engine.

dgallup

Sure, BMW might do those cruel tests to prove their engines can stand up to the ignorance and abuse of it's most extreme users. That does not mean it is recommended or ideal.

OP

Rod has it right. Common sense is all that is required. This is a stock factory engine I presume so it is designed to withstand the much of the abuse some users throw at it, however it is still desirable in my opinion to just keep the engine lightly loaded but happy.

I am not going to bother looking up your particular oil.

Also even if I did, I don't know how it compares to the recommended oil and I also won't bother looking that up.

The reason I asked if you where an engineer is that this site is designed for engineers to discuss engineering work related problems. The non engineers not welcome rule is so we don't get to bored spoon feeding clueless lay people with endless questions that to us are basic.

As you have been polite and not completely clueless you have not been red flagged and deleted despite your falsely claiming to be an engineer when signing up for the site.

Don't start expecting to much spoon feeding if you wish to stay. Also phrase your questions in a concise precise manner with all relevant detail, but no padding or to much flowery politeness. The guys here are often at work and have no time nor inclination for flowery small talk.

Regards
Pat
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RE: RPM on cold engine?

(OP)
Evelrod:
I get what you are saying, but if I change down, I will go over the limit of RPM's which I have been told to keep it under.

Benta:
Well, that is what I am told the name for it is. It is not the 2.5 from E34 with VANOS, but an engine from a whole other car. It is a 2.8 liter. I believe the car I took it from was an E39 cabriolet, but I can't seem to figure out BMW's way of naming their models, it's just ridicules.

My 2.8 is very weak at low RPM's, even with VANOS, which just adjust the valves when going low and high. Once I hit 4k RPM, it starts to deliver some power.

In Denmark such a car that I have is not very common, and really not with such an engine. Many people over here drives 1.6'es (My dad, Opel Astra F 1.6) It is only when we gather at friday night we see a few cars which is as powerful as mine.
Cars are not only expensive over here (180% tax when you buy a new one + the price of getting it shipped here and all that stuff.
But not only are the cars extremely expensive to buy, they are also extremely expensive to get insured. I pay about 4300 dollars each year, and the state also want me to pay what they call is "weight tax", there I pay about 1000 dollars a year.

Back to topic... My dad always lets his engine labour when it is cold, because he does not want to rev it. I can't imagine that is good for it, especially when it is such a small engine.

RE: RPM on cold engine?

Pat, fair comments; I think an oil pump drive failure or filter canister rupture would constitute a catastrophic bottom end failure, unless the engine was shutdown immediately.  If excessive oil pressure doesn't cause something to break, the result may be hydraulic lash adjuster pump up, which will tend to reduce rpm and hence oil pressure.

RE: RPM on cold engine?

(OP)
Thank you all for your advice.

RE: RPM on cold engine?

Greg

I was of the opinion that the heater bypassing the thermostat was for quick demist, hence safety, not passenger comfort.

The comfort aspect was simply a desirable side effect. The slower warm up was an undesirable side effect, but safety got priority.

Regards
Pat
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RE: RPM on cold engine?

Safety for society as a whole.  An individual's safety would be adequately served by not driving with frosted or misted up windows.

RE: RPM on cold engine?

I used to drive rental cars with the brakes on to increase engine load and get the heating working.

- Steve
 

RE: RPM on cold engine?

I think what I'm hearing in the background is a touch of youthful impatience.


Quote:

When I really push my engine by going sideways, it often starts to tick in the valves pretty quick, no matter what oil I use. I cannot imagine that it is good for the engine, and I am told that it shouldn't happen. I bet it can be pretty much anything, but when it only happens when the engine is working hard at high rev's (I never do this on a cold engine) may tell a bit about what it can be?
Never?  Or never below what temperature?

Suggests to me that oil is sloshing away from the pickup or that the pickup tube is otherwise able to suck air under those conditions.  If so, definitely not good.


Norm

RE: RPM on cold engine?

Norm, what you need to read is the original post.
There is no such thing as an M50B28 engine from BMW. The OP also admits that it's not original.
So, we're talking about a "Franken-BMW" here, probably a home-shop bored-out M50B25.

So all bets are off.

Cheers,

Benta.
 

RE: RPM on cold engine?

Umm, reading the original post is exactly what prompted the 'impatience' line of thought.  I've seen this particular topic from both sides of the coin, and it's apparent that there's some fishing for outside justification of his warmup technique going on, most likely to use the next time it comes up for discussion elsewhere.

The car make/model/extent of non-OE content is immaterial.

That said, upshifting a cold gearbox is apt to be easier if enough revs are reached just before upshifting, and this can easily mean briefly revving over 2000.  It's either that or double-clutch (the 1-2 upshift in particular).


Norm

RE: RPM on cold engine?

Benta,

Although that engine was not made by bmw, they exist so commonly now due to people building them, that they are a used engine number among the masses.

By what he is  saying re single vanos, his engine started out as a  M50B25TU, and then had 2.8 internal bits added to the block.

BUT having said that, he also did say that it came from and e39 ''cabriolet''  so god knows what it could have been.

I think the entire thread would have been better off on a Bmw forum to be honest, as he sounds young, and very ''new blood'' driving this ''sophisticated machine''.

Now had it have been a brm v16, where he would have had to machine new parts if the originals screwed up it would be entirely different. But in this case I dont think its anything to worry the op. The rear quarter panels may see 'wear' long before the hydro lifters.

Brian,

RE: RPM on cold engine?

I'm lucky to get any warm air from the heaters in my diesel on the way to work. If I take the "scenic" route, the needle lifts on my temperature guage and the heaters start to blow warm air.

For cold starts, there is a button I can use to switch on the front/rear window heaters, and the door mirror heaters. Otherwise, it just blows cold air at the side windows.

I have read/heard of diesels having heaters to suppliment the engine's heat for those few cold minutes, but it does seem a bit extravagant.

- Steve
 

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