Revving a cold engine

Thermal efficiency and stability. Cold oil does not flow well, cold cylinders do not atomize fuel very well. Also running tolerances are based on operating temps. Big gaps, low pressure.

 

Takes a minute or two to circulate. Then drive easy until operating temp is reached. Almost 20 min for a 575.Anyway the owners manual says no revs until operating temp reached. Bruce

 

I never sit in neutral and just rev my engine ?????
After a cold start it warms up for at least 10-15 min to operating temp.
I never understood what sitting still and slamming the gas pedal all the way down accomplishes ???? Revving it over and over ........
Please enlighten me

 

Oil temp is everything. Too hot or to cold is not good for engine life at all.

 

In the olden days, one might build a "race" motor with wide clearances and load the thing up with 50 weight motor oil.

An old dino 50 weight oil might have a viscosity of 1000 CSt at 32dF, whereas the running motor would have a viscosity of 20 CSt.

The old motor oils with paraffin in the not-too-refined oil had an interesting property, if loaded up with 2000 PSI of pressure, it would transition from a fluid that flows under pressure to a solid that does nothing under pressure. So, if you were to start the above engine with the above oil at -20dF and then floor the gas pedal, the oil separating the con rod Babbitt bearing from the machines steel crankshaft would "go solid and you stood a good chance of spinning a con-rod bearing or a main bearing.

 

Yes, oil viscosity and flow, but just as importantly, thermal expansion rates and tolerances.

Agreed. You have a lot of different metals and alloys in an engine - aluminum block, iron/steel/? cylinder liners, steel valves in aluminum heads, steel camshafts, forged crankshafts, titanium connecting rods, exotic alloy bearings - all with slightly different thermal expansion characteristics. The operating clearances are designed for the engine at operating temperatures - when cold, you will have some clearances too loose, some clearances too tight, causing premature wear if the engine is operated under load or at high speed.

Coolant temperature is a bad indication of an engine being warm - oil temperature is a much better indicator of all the internal components being at operating temperature when the oil temperature reaches about 190 F or so.

 

^^^This, exactly.

 

I think that these are race engines with a short life and often rebuilded.

Engines with really tight tollerances (f1 for example) are provided with a special pump system that pre-heated the engine oil before the engine start.

 

Surely once the operating temp had been reached.
Pete

 

Racing engines vs. Street engines - different things.... race engine may idle at 1K-1500 RPM
street at 800- 1000RPM

revving a race engine up - trying to get the metal up to temp, and close all the tolerances etc...

 

Another difference between a race engine and a street engine, beside the wider piston OD/cylinder ID clearance (to account for quick thermal expansion, as was mentioned) is that (at least in the old days) you would want to break in the cam at high speeds (but no load) as you had the best hydrodynamic lube-oil film.

But that is an exception, only for new engines (and maybe no linger valid). You should always warm up your engine somewhat. Unless you are in a hurry to get away from bad guys.

 

When I was young and stupid, I revved a cold engine because I was angry with it (it decided it did not want to start) ... a few trips later and it ran a bearing.

Only thing revving a cold engine does is hurt things
Pete

 

Oil viscosity is way off from the required values for good lubrication at cold temperatures.

There are some good indepth articles on the subject available elsewhere on/via fchat or google. Read them and you will possibly never dare to start your car again

 

There is a difference between reving a cold engine, and runnign a new engine(once warmed) hard to seat parts. There is the theory that todays engines are made with such great tolerances, and so little material to wear off that "running in" is no longer necessary to get all the parts to meet and work together properly. This theory holds that new engines should be run hard to best seat the rings and valves, that is after a warmup. This teory still does not explain how best to seat not quite perfectly round pistons in not perfectly round cylinders other than gentle run in.

Its alsio why in a rebuilt you should put each piston back in the cylinder it was born in.

On a cold engine, as many here have said thermal expansion of different parts and poorly flowing oil will greatly reduce engine life and you probably be wearing rings loosing hp and burning oil way sooner than otherwise.

Personaly I like to vary rpms while driving on a new engine, and after a few hundred miles slowy expandign the rev range, never lugging or revving in neutral(which is bad in all sorts of ways).

On the exige I just bought lotus recomends a 1000 mile break in, as did BMw on the M3 and I believe porche on the Gt3. Vipers also have a 1500mile break in period. Some say the break in period is really to force owners of these powerful machines to learn the car and take it easy untill they know how it goes.

In any event giving a modern engine 500 miles or ever exapnding rev and power ranges cant hurt.

Of course if youre leasing or flipping anew ferrari every few years, the harm done from cold revs may not be relevant to you.

On my elise which is an 8k rpm 4cyl motor it went to its first trackday around 400 miles, 7k track miles later it really does not burn a drop of oil. It has however always been properly warmed up, i wait till water temp up and then drive reasoanly till oil temp is up. I also religiously change the oil every 3-4 trackdays.

Not all oil is equal either, there is a big difference between mobil 1 10/40 and motul 8100 10/40. The mtoul is somethign like 4x the price for a reason. An elise they will eat the cams by 10k on track using mobil 1, but last indefinitely on motul. Of course it all depends on use.

From what i have read a motor running at sustained high revs as say on track has numerous hotspots and its those hotsports oil really needs to service. How an oil breaks down has to do with temperatures as well as shear impact etc.

Back to ferraris. I dont know what they recomend now, but in the old days (even BBis) the procedure was to let it warm untill you had some water temp, then to drive slowly ie no high revs untill the oil needle came off the peg, which usualy is 10 or so mins in.

I would say the worst thing you can do to an engine is to rev it cold, the second worst is to rev it to high revs in neutral. On the other hand if its fully warmed and has good oil in it, running close to redline as on track does no harm at all.

From what i have read, startup is when most wear occurs, now multiply that by revs.

 

Interesting explanation.
Exactly that happened to me on a bitter cold January night when my girlfriend was crossing over from the driver's side to the passenger's side(you young guys can Google "bench seat") moments after starting the engine and accidentally stepped down hard on the gas. Vroom,,,, da, da, da, da, da
I had always attributed this to pump cavitation.

Today, my special cars are allowed to warm until the temp gauge needle begins to move then driven gently until full operating temp. The "regular" cars are usually in drive before the starter is done spinning but driven gently while cold. I find the delayed upshifts for a cold engine in order to light the cats annoying and refuse to let the revs rise enough to do so(shift up) and usually wind up crawling for the first block or so.

 

This is one of the questions that to answer properly while covering all the various reasons and iterations of engine types would turn into an SAE paper a couple hundred pages long.

So the short of it, don't high rev cold engines, it's bad for them.

 

many race teams use engine preheaters and oil preheaters to get the oil viscosity to proper operating levels and the engine warmed to best temperature before start up
if there was no merit to the procedure, why are so many teams using the procedure

 

In Formula 1 they have to preheat the engines via the coolant and oil as the tolerances that the engines are built to results in them being completely seized solid when cold!

I would suggest that any race engineer/engine builder who revs the nuts off any stone cold engine is one to avoid!

 

So, in the context of this discussion, what's up with Ferrari's decision at the time to ramp the idle speed of the 308 2-valve injected series to something around 2800 rpm or so, in the name of meeting USA smog standards?

 

Probably to get heat into the converter(s) ASAP in order to reduce emissions. It's a safe bet it's not to enhance engine life.

 

Nothing wrong with that as long as the engine is fully warm before it's run hard. Any engine that is run in by the factory on a dyno was run hard as soon as it was warm. No need for low RPM break-in proceedures on modern engines. More here: Break In Secrets--How To Break In New Motorcycle and Car Engines For More Power

 

My understanding is that the old cast iron rings needed a prescribed break in. Cams and other parts served by splash lubrication are better served with more RPMs when breaking in.