RPM on cold engine?

[Jelle]

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

 

[patprimmer]

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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[evelrod]

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

 

[Lou Scannon]

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.

 

[patprimmer]

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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[BrianGar]

''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,

 

[dicer]

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.

 

[Jelle]

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.

 

[BrianGar]

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,

 

[patprimmer]

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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[Jelle]

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/p...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?

 

[dgallup]

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.

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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.

 

[SomptingGuy]

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

- Steve

 

[Jelle]

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.

 

[SomptingGuy]

heaters working = thermostat open = nice warm engine

- Steve

 

[LionelHutz]

heaters working = thermostat open

No it doesn't.

 

[SomptingGuy]

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

It is, you know!

- Steve

 

[evelrod]

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

 

[Compositepro]

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.

 

[benta]

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...)