Engine wear driving slower or faster???

[35Remmy]

We were talking about this the other day in the garage and I wanted to know what you guys think....

2 vehicles have to travel 100 miles.

1 car does 80MPH for 100 miles
1car does 65MPH for 100 miles

Who is wearing their engine more?

1 is getting there faster; however, the slower car has to run its engine longer.

 

[Explorer_Phil]

Well...

Technically, if the vehicle is a manual, then the vehicle will go through the same number of engine revolutions no matter the speed becasue no matter what happens, the vehicle went 100 mi. If it is an automatic, there is a small amount of energy lost in the fluid transfer of the transmission, meaning that the 85MPH one would work slightly harder.

Now if you want to get into the weeds about how a slightly increased operating temperature from the higher speed, more use on the valves and other moving parts due to the greater gas comsumption, and other small factors like that affect the engine, then I think the 80MPH one actually works a little harder.

Now, how much harder is something for an efficiency engineer somewhere.

 

[35Remmy]

I don't understand how if the vehicle is a manual, "then the vehicle will go through the same number of engine revolutions no matter the speed becasue no matter what happens, the vehicle went 100 mi."

I mean, you would be in 5th or 6th gear, but the engine RPM's would increase (more work) as the speed increases, right? Higher RPM's-->higher revolutions

That's just how I'm thinking about it.

 

[Explorer_Phil]

I'm saying that, mathematically, if both gear ratios are the same (for the 80 MPH vehicle and the 65MPH vehicle), then they have to go the same number of revolutions to go the same distance if they are in the same gear.
If you think about it, in the highest gear, each revolution of the engine moves the driveshaft the same distance, therefore, 100 miles would take the same number of engine revolutions for either vehicle if in the same gear. The only thing that changes is the amount of time it takes to go the distance becasue the one engine is revolving faster than the other. Higher RPMs = higher speed, not greater distance.

 

[35Remmy]

Ahh...good point...that does make perfect sense now.

 

[ThePhoenix]

i can tell you who is getting crappy gas milage...

 

[gijoecam]

From a number of revolutions standpoint, yes, wear would be identical. However, in general, the engine being asked to go faster will be consuming more fuel, and will be 'working harder'. More fuel = more force in the combustion chamber = more force on the conn-rods, wrist pins, bearings, crank, faster moving camshafts, valves, etc.

All other things being equal (and that's the important part), I would say that the engine working harder will experience more wear.