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Originally Posted by blue2000s
Strictly speaking, if the loads and engine speeds are the same and there are no other differences but vehicle speed, there would theoretically be no difference in the wear on the engine given a set amount of time. The total miles on the car would be different, but that wouldn't matter to the engine.
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Hi,
That's just it, it's the loads which make the difference, not the revs. 5k RPM on level ground places much less stress on the engine than 5k RPM on an incline.
The car going 5k RPM on level ground will also experience a lot better MPG, because it's doing less
WORK than the one going up the incline at 5k RPM.
Now, all this assumes that the gearing is the same for each. Because it usually isn't, any less rolling resistance/friction/mechanical inefficiency experienced by the car at highway speeds than the one operating at 35MPH in a shorter gear, will be offset by the increased drag which rises by the square of the speed the car is traveling.
The reasons a Highway driven car is preferable to a street driven one is that:
a.) It has less time/stress on it per mile than the street driven one.
b.) It has spent more of it's life with the Coolant Pump, Oil Pump, (both Crank Speed dependent) operating at their most efficient speeds. Also, Radiator Airflow, Alternator output are also in their sweet spots. And, these conditions remain constant throughout the drive, or at least much more so than for a street driven car...
Happy Motoring!... Jim'99
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