Engine wear - revs vs rpm

[rationull]

I've been curious about this question for a while, and maybe some of you here more knowledgeable about engines know the answer. Assuming an engine is operating at a reasonable speed (for the sake of argument, lets just say under redline), does higher engine speed actually result in appreciably higher wear?

For example, if a given car is traveling on the highway in top gear, is there a legitimate difference in engine wear at, say, 80 mph at 3500 RPM vs 60 mph at 2500 RPM? Of course, there's a large difference in air resistance between 60 and 80 so you may see increased wear due to increased load, but the question still stands in cases where the speed difference isn't quite as great (e.g. towing, or ascending/descending grades in a lower gear).

If you're going a specific distance, the engine will rotate the same number of times regardless of how fast it's turning (assuming you stay in the same gear, assuming a directly coupled transmission, etc). Does that mean the wear is going to be roughly constant for a given trip, or do you see increased wear just because the engine is spinning faster?

 

[gmchevroletruck]

there would also be increased load at lower rpms vs higher rpms in many cases, depending on the torque curve of the motor...something else to add to the equation. I think about this stuff as well, or have in the past. At this point, I have settled on: staying away from "lugging" the engine, and just driving at my desired speed. I'm not likely to alter my desired speed of travel based on the theoretical effects on the motor (within reason), I'm more concerned about when I arrive in most cases. But I do have a tendency to "baby" the motor most of the time, with slow acceleration, and rarely go over 75mph (2200 rpm in my case). I'll probably end up with a stuck ring from the light accelerations, especially with an automatic transmission.

Good topic.

 

[Petrou]

Heres another one to think about. When you are traveling at highway speeds. and your motor is running at say 2300-2400 in my case. The oil pressure and oil is running through at its highest pressure. it is able to produce its maximum amount of film to protect parts at idle it produces a low amount of film creating more wear. this is why there are severe service and normal service intervals. city and stop and go severe running down the highway 90% of the time, normal service

 

[mva]

I stay away from lugging.

I also stay away from high revs until the engine is fully warmed up. BMW recommends keeping the RPM under 4000 until the oil temperature is at least 60C. It takes at least 10 to 15 minutes to reach this temperature even in spring/summer on my 2000 Z3M - longer if it is cold.

Some BMW's even have a variable redline depending on temperature. I don't totally understand why but I have read that it is dangerous to start up an engine and immediately rev it up to the redline.

 

[Bryanccfshr]

I equate wear to load and shock load. So of course driving faster or pulling a trailer increases load and these slightly increase the rate of wear. Running the engine in a gear lower at the same speed within reasonable RPM parrameters should cause no real negative effects. Driving at maximum output all the time will significantly shorten the life of an automotive engine. In most normal day to day driving they rarely use 50% of their power usually much less. Now if you floor the throttle and accelrate as fast as possible every time and pop the clutch(shock load) you can expect shorter engine life.. This is the difference between spirited (but concious)driving and abusive driving.

An engine can perform a certain amount of work in its service life. You can use that work quickly through severe duty cycles towing or pushing the engine or you can extend the life of the engine by only using the power out put as needed.

Some engines have the high power inputdesigned into them while most economy minded engines have a great max output but the engine is not desinged to put that out on a reutine basis. If it is, it will wear out or due to metal fatique and economy based metallurgy fail in an ugly way.

 

[gmchevroletruck]

+1

I tell my brother (speed racer) that, any engine only has a certain amount of total power to give, and if you spend it all at once it will go broke. Sometimes folks have to learn this the hard way.

I also go very easy on the rpms until the engine is fully warmed up...which is difficult because I live right on a 55mph highway. I just wait for a clearing, pull out and accelerate extremely slowly - it takes me 2 miles to get to 50 mph. Hey, if they don't like it, they can go around lol...none of these folks are going to buy my next car. Unless of course I get rear-ended doing this...lol

 

[defektes]

Theres a pretty big hill here where I live and I drive at 80-90 mph normally. it forces me to shift into 4th and i go 4 or 5 miles in 4-5 RPM's my engine is still fine ^_^

 

[KrisZ]

Higher RPM is not a problem as long as the engine is fully warmed up. If your engine has a 6500RPM redline and you are traveling at say 3000 or 3500 rpm, it's only half way of your rpm range.

 

[mjoekingz28]

Originally Posted By: gmchevroletruck
+1

I tell my brother (speed racer) that, any engine only has a certain amount of total power to give, and if you spend it all at once it will go broke. Sometimes folks have to learn this the hard way.

I also go very easy on the rpms until the engine is fully warmed up...which is difficult because I live right on a 55mph highway. I just wait for a clearing, pull out and accelerate extremely slowly - it takes me 2 miles to get to 50 mph. Hey, if they don't like it, they can go around lol...none of these folks are going to buy my next car. Unless of course I get rear-ended doing this...lol




That is rediculous, you should lose your license.

 

[rationull]

Originally Posted By: mjoekingz28

That is rediculous, you should lose your license.


Your rhetorical style intrigues me.

 

[Tosh]

A book I have says wear increases with the square of the relative speed of the surfaces, all else being equal.

 

[fdcg27]

I think that common sense tells us that higher revs should produce more bore and ring wear, with maybe a little higher bearing wear, both crank and cam.
I do know that we sold our very short geared '76 Civic 4sp 1500 at 160K, and even then, no make-up oil was required on 3K changes with the 10W-40 available way back when, so this may not be such a simple question.

 

[BuickGN]

Originally Posted By: Petrou
Heres another one to think about. When you are traveling at highway speeds. and your motor is running at say 2300-2400 in my case. The oil pressure and oil is running through at its highest pressure. it is able to produce its maximum amount of film to protect parts at idle it produces a low amount of film creating more wear. this is why there are severe service and normal service intervals. city and stop and go severe running down the highway 90% of the time, normal service


Oil pressure and film may be reduced at idle but so is the load. I'm pretty sure an engine would last longer idling it's whole life than towing a trailer.

 

[GMFan]

This thread reminds me of a LOL moment I had today. On the highway this late 1980's honda civic merged onto the highway like a man on the run....the car was obviously floored as it was spewing burnt oil out the exhaust. It was so bad you could smell the car even 100 yards ahead. When they'd accelerate real fast you woulds see a HUGE plume of smoke and a few sparks or two from the engine backfiring...you could even hear it go POP when he got on the accelerator.

Of course he was beating the heck out of it and it was lowered with all kinds of tacky stickers on it.

I wondered how many miles were on it and how much oil it was burning. I've never seen such an oil burner.

 

[BuickGN]

When talking about high rpms, it's not just the immediate stress you're putting on parts but the total number of revolutions.

What would you expect to last longer, a car with OD that spends it's life cruising down the freeway at 1,800rpm or a car with no OD that cruises at 3,600rpm. Regardless of theories, one car has made twice as many revolutions as the other over the same distance.

 

[Gary Allan]

Quote:
I'm pretty sure an engine would last longer idling it's whole life than towing a trailer.


Probably so, but how are you measuring the work? You'll retire before the engine stops running due to some worn out part idling.

You might not last much longer in terms of fuel.

 

[rationull]

Originally Posted By: BuickGN
When talking about high rpms, it's not just the immediate stress you're putting on parts but the total number of revolutions.

What would you expect to last longer, a car with OD that spends it's life cruising down the freeway at 1,800rpm or a car with no OD that cruises at 3,600rpm. Regardless of theories, one car has made twice as many revolutions as the other over the same distance.


That's exactly the point I'm trying to get at with this discussion, though. I'm taking it for granted that more revolutions means more wear, and thus when cruising on the freeway at 65 mph, my car is better off in 5th at 2900 RPM than in 4th at 3600 RPM -- that much seems clear.

But, what if the choice is between 5th at 65mph/2900 RPM or 5th at 80mph/3500 RPM? Assuming I'm going a set distance either way and can't choose the top gear ratio, I'll be turning the engine the same number of revolutions in either case -- and my question in this post is, is the engine actually worse off at higher speeds in this case?

 

[Ben99GT]

Originally Posted By: rationull
That's exactly the point I'm trying to get at with this discussion, though. I'm taking it for granted that more revolutions means more wear, and thus when cruising on the freeway at 65 mph, my car is better off in 5th at 2900 RPM than in 4th at 3600 RPM -- that much seems clear.

But, what if the choice is between 5th at 65mph/2900 RPM or 5th at 80mph/3500 RPM?


Higher rpms equates to higher piston speeds, which equates to higher rod, rod bolt, and wrist pin loads, which equates to higher rod bearing loads, which equates to higher crank loads, which equates to higher main bearing loads, etc. Low load/high rpm conditions result in more stresses and wear than low load/low rpm conditions.