OT: Redlining cold engines

[Malakas]

I was told what really hurts the engine when it's cold is "load". Revving the car to 5-6k when cold, stationary, and in neutral - should not really be harmful. In fact u see racing mechanics run out to paddocked cars - start them, run them through the rev range, and shut them off.

When I had a S2000 if I blipped the throttle after starting it - I'd swear it would warm quicker once I drove away.

But as said above - I would never put a high load on a cold engine - so I never drive over 3k unless car is up to temp.

[Tippy]

Originally Posted by Orient Express

I have seen a 996 engine with only 500 miles on it, with a thrown rod from redlining it when before it fully warmed up.

Sure, the engine hasnt had enough cold runs to make a good wear pattern yet. I bet if it were 5k miles, the motor would still be around IMO.

[Tippy]

Originally Posted by Malakas

Revving the car to 5-6k when cold, stationary, and in neutral - should not really be harmful.

In fact u see racing mechanics run out to paddocked cars - start them, run them through the rev range, and shut them off.

First part, I would think opposite from what I was "taught".

Second, why do they do that? What's the reasoning? Just curious.

[Torontoworker]

Thermal shock is a fact in northern climates. Back in the day when I had to travel WAY north of where I live - as in 12 hours north - you would wake up to an air temp of -40F and even with the car plugged in to an AC outlet (without it - wait until spring!) you could hear all sorts of weird sounds for the first few minutes as the coolant in the top of the motor (heater OFF to warm up quicker!) met different areas of the motor that were warming up faster I guess. I'd sit there, the seats made out of ice cold cement (no heated seats!) scraping off the inside of the window wondering how much lubrication I had with semi solid oil trying to flow from the back of the pan and into the oil pick up. I didn't even want to think about what would happen if I rev'ed up the motor! (Another reason other then salt to hibernate my toy until April!)

Now this IS extreme but the idea of allowing your motor's internal parts to all reach a uniform temp before high RPM's is valid. We also have issues of very cold gas from the tank and running through injectors into hot cly's to worry about up here in sub zero weather as I have heard of people breaking rings in the first minute after starting the car in these conditions. I bet 0w 0 would sell quite well up around Cochrane Ontario in the winter months!

[BruceP]

My understanding has always been that the mechanical argument for warming it up by driving it was that it avoided uneven heating and hot spots.

But I also know that this practice was originally encouraged for emissions reasons. Idling is obviously not very green, and the cats don't work until they're hot. A lot of stuff like oil change intervals, viscosities, startup procedures, timing and mixture settings, etc. have nothing to do with performance or reliability. It's all about emissions compliance.

[Tippy]

Originally Posted by Torontoworker

Thermal shock is a fact in northern climates. Back in the day when I had to travel WAY north of where I live - as in 12 hours north - you would wake up to an air temp of -40F and even with the car plugged in to an AC outlet (without it - wait until spring!) you could hear all sorts of weird sounds for the first few minutes as the coolant in the top of the motor (heater OFF to warm up quicker!) met different areas of the motor that were warming up faster I guess. I'd sit there, the seats made out of ice cold cement (no heated seats!) scraping off the inside of the window wondering how much lubrication I had with semi solid oil trying to flow from the back of the pan and into the oil pick up. I didn't even want to think about what would happen if I rev'ed up the motor! (Another reason other then salt to hibernate my toy until April!)

Now this IS extreme but the idea of allowing your motor's internal parts to all reach a uniform temp before high RPM's is valid. We also have issues of very cold gas from the tank and running through injectors into hot cly's to worry about up here in sub zero weather as I have heard of people breaking rings in the first minute after starting the car in these conditions. I bet 0w 0 would sell quite well up around Cochrane Ontario in the winter months!

Yeah, wrapping a motor to redline cold in the North would more than likely have catostrophic effects 100% of the time. In the South where I live, probably be ok even in the coldest conditions.

Originally Posted by BruceP

My understanding has always been that the mechanical argument for warming it up by driving it was that it avoided uneven heating and hot spots.

Hmmm. I am trying to figure out how this would create uneven heating. So, your combustion chamber and exhuast side of the engine would be hot while everything else is cool when idling to operating temps. This would be the differentiation I'd assume.

So, does the friction from (friction bearing, metal to metal contact) loads really warm up the engine that much quicker or is it the heat dispersed from combustion that ultimately is responsible for engine temps?

If it is the former, then I could see uneven heating.

We never got that into depth in school for aviation reciprocating engine theory (same as a car engine).

[peavynation]

Good thread.

I remember seeing a graph in an HP Engine Series book on the Ford FE that showed Engine Wear Vs Water Temp. Very interesting! I know we're all in agreement that "cold running" and "engine wear" go hand in hand, but here is a graph of similar data to what I saw way back when. I love the internet.

So the hotter the engine the better it is on wear, from a metallurgical stand point. But excessive heat can and will adversely affect other aspects.

Food for thought. And, being an engineer, I love data.

[Torontoworker]

Originally Posted by Tippy

We never got that into depth in school for aviation reciprocating engine theory (same as a car engine).

Funny you mention that. Driving around in our sort of tundra like weather I recall a car I was driving up north was suffering from what aviation people would say was 'carb icing'! Nothing you could do about the problem other then drive it in a lower gear and rev the **** out of it to produce as much heat as you could. Just like a Cessna at 10K and dropping alt from icing - my car was chugging along slower and slower as the intake iced up. I ended up stuffing newspaper in between the rad and the grill, blocking part of the ram air intake and driving without the heater on for over 200KM! Fuel injection was a god send in our part of the world.

[Deepsix]

I just swapped from a supercharged genuine 500HP mustang to a 2004 996 and IMHO warming up should be done on the move, BUT redlining, in the Mustang anyway was a recipe for throwing a rod, it will always be the weakest component that goes first! Here in Texas it never gets that cold anyway and the motor warms up in a mile or two, until then I keep below 4000rpm

[fpena944]

In my case I try to keep the revs down and won't go to redline but to keep it below 5k rpm is tough for me...Reason being that where I live there is a divided four-lane road that I must take a left on. So in order to make it out of my neighborhood I need to give it a little throttle in order to get the car going at the same speed as traffic.

It's far from redline but also a bit above the 3k-4k limit some say to keep it under. Granted these aren't sub-zero temperatures I'm starting off from and I do have 0w-40 in the car but I do see the oil pressure gauge is pegged at 5 bars during this maneuver.

Hopefully it won't make too much of a difference but my only option is to let it sit there for twenty minutes while it warms up fully.

[BruceP]

Originally Posted by Tippy

Y
Hmmm. I am trying to figure out how this would create uneven heating. So, your combustion chamber and exhuast side of the engine would be hot while everything else is cool when idling to operating temps. This would be the differentiation I'd assume.

So, does the friction from (friction bearing, metal to metal contact) loads really warm up the engine that much quicker or is it the heat dispersed from combustion that ultimately is responsible for engine temps?

If it is the former, then I could see uneven heating.

We never got that into depth in school for aviation reciprocating engine theory (same as a car engine).

You have me at a disadvantage.

As I said, this is the story I've always got about this. I think it's even come up on threads here or on Renntech. Either way, I'm bringing a knife to this gunfight.

[Granger968]

4-corner piston scuffing is a risk if you over-load at low operating temperatures. Piston will grip the liner at four "corners", leave some marks, then high oil consumption if you're lucky, a seized piston if you're not. The piston doesn't take the right shape until it's up to temperature.

Starting the car "cold" and opening it up for a quarter mile is not the best idea. That being said, I don't think there is any issue with starting the car and headed for the grocery store right away...

My 2 cents...

[Tippy]

Originally Posted by Granger968

4-corner piston scuffing is a risk if you over-load at low operating temperatures. Piston will grip the liner at four "corners"

Not sure how much distortion the liner exhibits once the head is torqued.

I know air-cooled aviation motors have a tight fit in the liner towards the top and then looser fit towards the bottom when cold. Once at operating temp, the liner is supposed to be as linear and straight as possible for the piston to travel in. This is due to the most amount of heat residing in the top of the bore.

[redridge]

The truth is... its the amount of time that the car reaches to temp. When you redline an engine when cold... The delta temp of various parts of the engine will be at its greatest... There will be cold spots and hot spots.... gradually bringing the car up to temps reduces stress on an engine. This is one of the reason why the 2 radiator line intersects each other so that the delta temps between the 2 rads would be a wash...

Oh, did I mention I stayed at the Holiday Inn last night...

[autobonrun]

My suggestion is not to redline any engine until the oil reaches operating temperatures. Oil pumps put out flow and that's related to viscosity. The colder the oil, the thicker the oil and the less the flow for a given pressure. Porsches in particular have tight tolerances between moving parts and require sufficient oil for lubrication. It's not to say you'll have a catastrophic failure; it just is not optimum lubrication as the engineers designed when the engine is cold.

On my M5, the engineers provided lights inside the tach that show maximum recommended RPM until the oil reaches operating temperature. They start off with a max recommended rpm of 4k when cold then they gradually go off as the sensor in the oil pan detects the oil has reached operating temperature. Eventually, they all go out except the last one at 7k rpm.

This photo shows some of the lights off because the oil is warm. When totally cold, they are all on initially.