Does engine wear increase exponentially with higher RPM? (car engine, valve, seats)

[RobertFisher]

I always have this impression that it does. I it may be from the old Gastrol ad that has engine running faster and faster and at high RPM it stops and shatters. Is there conclusion on this question?

Case study: running the engine at 2000 RPM for 500 hours, vs. running the same engine at 5000 RPM (still outside redline) for 200 hours, each will have the engine turn 1 million times. Does one produce more wear than the other?

[Igor Blevin]

Well, 60 million revs, but same point.

My understanding is that engine wear is caused by revs and heat, so if the engine is running hotter at 5000 RPM than at 2000 RPM in your example, the high reving wear is greater. If your engine is running at the same temperature in both cases, then you would have the same wear.

So the question is, do car engines run hotter at higher RPMs? You would think they would generate more heat at higher RPMs as they are doing a lot more work per unit time, but if the speed of your car allows the radiator to change out that heat, then maybe not.

If you are talking about 2 engines sitting on blocks in your garage with one run at 2000 RPM and the other at 5000 RPM, then the high revving engine should be running hotter, but cars don't work that way. Usually you are driving faster and have the benefit of better heat exchange through the radiator.

As far as exponentially greater wear, I have no clue.

[YourWakeUpCall]

At 5000 rpm, the internal surfaces of the engine (yes, I know there is an oil film between the surfaces) are rubbing against each other 2.5 times faster than at 2,000 RPM. Unless there is some magic lubricate whose protection increases with with friction, it's safe to say that an engine will wear faster at 5K RPM than at 2K RPM. An order of magnitude faster? Maybe. Maybe not. 1 order of magnitude is 10 times faster. That seems like a lot. It also depends on the engine. My guess is that an engine with a redline of 4,500 RPM isn't going to last as long as and engine with a redline of 10,000 RPM if both were held at a steady 6,000 RPM. So, does an engine wear faster at higher RPM? Probably? An order of magnitude faster? Too many variables to say.

[RetireinPA]

its been a few decades since I bothered to run the calculation, its likely still buried on the SAE website but yes, the wear is proportional to the square of the RPM

[marlinfshr]

I know when it comes to diesels on boats, the charter guys running at 2000 RPM's (on an engine that maxes at 3500ish) typically get 3 to 4 times as many hours before rebuilding as the private guys running the same motors at the "recommended" 2950 RPMs.

Likewise, outboards being run at low RPM's, typically commercial operations, can go 5000 hours or more. But many mechanics and even the outboard manufactures always insist on running them towards the top often and keeping them around 4500 rpms or so typically. And outboards have a reputation of being done at 2000 hours. I wonder why. If the commercial guys only got 2000 hours out of a motor, they wouldn't be able to afford to live. I put 1800 hours on mine in the past 2 seasons!

[burdell]

Originally Posted by YourWakeUpCall

At 5000 rpm, the internal surfaces of the engine (yes, I know there is an oil film between the surfaces) are rubbing against each other 2.5 times faster than at 2,000 RPM. Unless there is some magic lubricate whose protection increases with with friction, it's safe to say that an engine will wear faster at 5K RPM than at 2K RPM. An order of magnitude faster? Maybe. Maybe not. 1 order of magnitude is 10 times faster. That seems like a lot. It also depends on the engine. My guess is that an engine with a redline of 4,500 RPM isn't going to last as long as and engine with a redline of 10,000 RPM if both were held at a steady 6,000 RPM. So, does an engine wear faster at higher RPM? Probably? An order of magnitude faster? Too many variables to say.

But, think about taking an engine apart and finding the most cylinder wear near the top of the stroke where the piston speed is slowing down and hitting zero before it starts its downward journey.

[Northrick]

Originally Posted by burdell

But, think about taking an engine apart and finding the most cylinder wear near the top of the stroke where the piston speed is slowing down and hitting zero before it starts its downward journey.

But it does the same thing at the bottom of the cylinder - slows, stops and reverses. I suspect more wear near the top is due to less lubrication at the top.


The thing you point out though, is that with a piston engine, both the pistons and the valves come to a complete stop and reverse directions many times a second. The faster the engine is spinning the higher the stresses are on numerous components (connecting rods, valve seats, bearings, etc.). Higher stresses lead to higher wear.

[Listener2307]

Originally Posted by RobertFisher

Does engine wear increase exponentially with higher RPM?

Intuitively, I say, "Yes". I say yes because at a lower RPM it takes less force to yank the piston up and down.
You and I could lob a baseball back and forth to each other for days on end.
If we fired it back and forth someone's arm or someone else's glove would wear out.
But that's all intuitive; I have no real information.

[king john IV]

exponentially?
depends upon
the exponent.

[burdell]

Originally Posted by Northrick

But it does the same thing at the bottom of the cylinder - slows, stops and reverses. I suspect more wear near the top is due to less lubrication at the top.


The thing you point out though, is that with a piston engine, both the pistons and the valves come to a complete stop and reverse directions many times a second. The faster the engine is spinning the higher the stresses are on numerous components (connecting rods, valve seats, bearings, etc.). Higher stresses lead to higher wear.

I think much of it is also do to more heat. There are so many intertwined factors in what this discussion's about I'd think it extremely difficult to come up with rules having few if no exceptions.