Safe RPM for a cold engine

[obi_waynne]

We advocate respect for an engine when it is cold. Obviously the limits will vary a lot from engine to engine but I was wondering what you consider to be a safe RPM to use on a cold engine?

So how low do you keep your RPM when the engine is cold and for how long for?

When do you consider an engine to be warmed up? (Needle out of the Blue or only when the car is at the usual running temperature?)

I stick to 2000rpm when cold and move upto 3000rpm when the needle moves out of the blue, only when my car is up to the usual 90 odd degrees will I use the rest of the RPM range. Am I being a bit paranoid or too harsh?

 

[BAD63R]

2500rpms are usually ok, maybe slightly lower if you have a turbo. Most places will say that 3000 is safe but i just like to be sure

 

[marti5]

2000 and under is good until its warmed up.....

 

[HDi fun]

It does depend very much on the engine concerned. Oil circulation is one issue. An oil temperature gauge is useful here - my 406 had one as standard and, having never had a car with one before, it's startling how much longer the oil takes to reach normal temperature than the coolant does. At least, for that particular car.

Probably more significant is the fit between pistons and bores. As the engine warms up the pistons expand slightly, so clearly, until warmed up they are a loose fit in the bores.

As well as not revving too hard I think it's more important not to apply too much load to the engine

So it might be better to run to 3500rpm in 2nd during warm up but under very light throttle pressure rather than to change up to 3rd at 2000rpm and then have the engine working hard at 1200-1400rpm.

I'm basing this upon petrol engines which generally rev a bit higher than diesels, but the same principles apply.

 

[MasterAuron]

I agree with HDi, it's about load as much as RPM. No point in trying to keep it under 2000rpm if you're having to give it a fair bit of acceleration to go anywhere. On the GT I let it idle for a few minutes first then keep it under 3000rpm and use very very light throttle so it doesn't boost. If I kept it under 2000rpm and pressed too hard on the peddle to go anywhere it'd start spooling up, not good on a cold engine!

 

[obi_waynne]

Are we talking 1/3 to 1/2 throttle then?

 

[HDi fun]

Are we talking 1/3 to 1/2 throttle then?

Blimey no - much much less initially.

 

[turbonutter69]

I keep my Focus under 2000Rpm and it will happily cruise along. I live in some tight back streets so I can't go fast anyway.

 

[HDi fun]

2000rpm in the deceased 406 was slightly over 70mph in top gear.

 

[turbonutter69]

Mine will do roughly 40-45 in 5th.

 

[HDi fun]

Doesn't your Focus have a 6th?

 

[turbonutter69]

Nope it's only a tiny 1.6.

 

[RobBentley]

I tend to keep both the W8 and R36 under 3000rpm under light throttle.

Unfortunately (for engine kindness) our Freelander TD4 is a CVT Automatic and has a low redline of 4k/rpm - and you've no real control over the revs. They tend to fly up to one place and stay there under pretty much any throttle load (as you would expect a CVT to do).

 

[pgarner]

try and keep it around 2500rpm and on light throttle. use the oil gauge as indication normally waiting till it shows 180 F (around 80C )this is normally 3-5 mins after the water is showing 90C

 

[old-git]

Probably more significant is the fit between pistons and bores. As the engine warms up the pistons expand slightly, so clearly, until warmed up they are a loose fit in the bores.

Isn't this the wrong way round? F1 engines can't be started from cold as the pistons are too tight in the bores. They have to be pre-heated so that the block expands enough to allow the engine to turn over.

I think

 

[HDi fun]

Possibly in F1 that is the case although I thought is was to do with the oils that are very viscous at ambient temperatures (F1 engines don't use multigrade oils).

Let's look into this re. F1. I can tell you for a fact that it is loose fit with road engines - what else would account for piston slap on cold days.

 

[old-git]

Possibly in F1 that is the case although I thought is was to do with the oils that are very viscous at ambient temperatures (F1 engines don't use multigrade oils).

Let's look into this re. F1. I can tell you for a fact that it is loose fit with road engines - what else would account for piston slap on cold days.

On checking this morning, I was talking c**p. The pre-heating of F1 engines is due to no big end bearing clearances when cold, nothing to do with pistons - memory fade.

Both the pistons and block expand, although at different rates. Aluminium expands at about twice the rate of steel. Don't know about cast iron, but if this is the same then it supports what you are saying.

 

[HDi fun]

Cast iron has a very low thermal expansion co-efficient. Pistons are almost universally of aluminium so that fits nicely.

I never knew that the bottom end of the engine was that tight when cold in an F1 engine.

How does that work then? I suppose the rods must be made from a different material to that which the crank is made from.

It's time I did some research into F1 it appears.