Is there "more stress" on the powertrain to run at a higher load?

Example on an automatic transmission. We can control it with our throtle position. Is it better to run at 5th gear at 45mph and 1,900 rpm. You can feel the vibration a bit more.

Or run it at 5th gear at 55mph at 2,300rpm. At which the powertrain feel smoother.

The above numbers are just examples to show two different situations.

In this case, does the higher engine load and/or less rpm gives you better MPG? Or does it cause more stress and wear?

 

More stress and wear. The idea is to keep it in a gear where power delivery is the smoothest to ease the wear and gas consumption.

 

Yes...the "load" is working against the engine, so there is more stress...that's like trying to run in air where there is no load, and trying to run in a swimming pool where there is more load working against you.


What is "better"? Better for fuel economy or for engine response? For fuel economy, the 45mph at lower RPM is better because you are using less fuel to maintain a certain speed. At 55mph, you are working harder against air/friction/etc. to maintain that speed, hence higher fuel consumption and higher stress. For engine response, it depends on the engine because the powerband differs from engine to engine...at 2300rpm the engine may be producing more torque than at 1900rpm.

As for vibrations, that also varies because some engines/cars dampen things differently...vibration frequency increases at higher engine speeds, which is where things start to "buzz" more than vibrate. At lower engine speeds, the frequency is lower and is more pronounced (e.g. bass in music has lower frequencies, so "vibrations" are deeper and more pronounced while higher notes vibrate at a higher frequency...unless you have no highs or lows, then you must have a bose). I would not equate vibration to "load" though...higher vibration frequencies may result in more load due to how fast things are moving back and forth than lower vibration frequencies where things are moving slower, even if the higher vibrations "feel" smoother.

generally, higher load (like driving uphill, maintaining faster speed) gives you worse MPG and causes more stress and wear than lower RPM and cruising at lower "loads".

 

depending on if it's gasoline or diesel, how many cylinders, how much torque/hp and what redline is will make a difference.

you can do a lot of damage if the rpms are low and it's bogged down. each car is really different.

 

depending on the throttle position and the speed, i shift in SS mode...i usually shift early to get better gas mileage....

shift from 1st ot 2nd ~ 7-8 mph
2nd to 3rd ~ 15-18 mph
3rd to 4th ~ 25 mph (you can shift at 20mph but the car kinda vibrates...so i give it a little more before shifting)
4th to 5th...now this is tricky....if i am going down a slope then at 40 mph....if up a slope then at 50mph....and if in a straight line then 45-ish mph....

this should reduce the load of running on a higher gear with lower rpm...