Engine health. High load high gear vs high load low gear

[nick666]

This isnt about consumption. Its about engine health. An automatic changes into a lower gear depending on how much you press the throttle.

The consensus among the drivers I know is that if you press hard on the pedal you should change into a lower gear otherwise it damages the engine, the lubrication being inadequate for high loads on low rpm.

Is that true ? Is it really damaging on the engine ? Isnt this only about that point where the rpm is so low that the engine makes that specific ugly vibration and noise (usually below 1000-1500 rpm)?

[Frank Lee]

If it's not lugging it's fine.

[user removed]

With a cranking RPM of 100, my original 37 Ford flathead would produce 60 PSI of oil pressure before it ever started. I used to crank it (starter button) with the ignition off when it sat for week or longer to get some oil circulation.

Lubrication related failures are virtually unknown in modern engines with decent maintenance.

The "ugly vibration" which should only occur in a manual is just the engine "telling you" it's time to downshift. If that communication is ignored completely, it would still take quite some time for any significant damage.

Frank referred to "lugging". In modern fuel injected engines the really dangerous component of lugging which in the old carbureted days was accelerator pump enrichment without adequate engine speed, no longer exists. I'm not saying there would be NO damage but with efi, you don't have the accelerator pump component.

Automatic transmissions work by imputs for vehicle speed and engine load, so they really don't allow lugging.

regards
mech

[JRMichler]

A big reason for the gas mileage I'm getting from my truck is that I do a significant amount of driving at 600 to 1000 RPM in fifth gear. The ignition timing goes to zero degrees (TDC) at low RPM and high manifold pressure, so no lugging. It does shake due to the torque pulses. The truck went over 90,000 miles recently and the engine is still in excellent shape.

[awcook]

My Civic shakes whenever I stop while in gear. This usually happens whenever I get off of the highway and shifting to Neutral will stop the shaking. I think that it could possibly be the radiator that shakes the car, but I'm not sure. Is this a bad thing for automatic transmissions?

[serialk11r]

Tell that to Mercedes, their engines produce tons of boost at barely over 1000rpm. I'm not scared of hitting the gas. If the engine is cold then yea I'll be careful.

[ShinyMew]

I am glad this question was asked. There is a steep hill around 300m long that I have driven up and over more than one thousand times. Each time I travel up it I challenge myself to hold the gear for the entire ascent. There are some noticeable vibrations from the vehicle, made in 1992, as the RPMs slowly fall lower and lower and my pedal pressure simultaneously reduces, but I'm not sure what would indicate this to be 'lugging'. Only twice have I ever ascended it completely whilst holding the one gear, alas.

[user removed]

ShineyMew

My response to your scenario would be to begin the ascent at the highest speed I could comfortably allow, given the consequences, then allow that speed to drop off slowly while staying in high gear as long as possible.

If your car is an auto then lugging is virtually impossible. If manual then it is possible.
I think 1 k rpm is fine and modern fuel injection will not allow the flooded component of a carb with accelerator pump being floored at too low an rpm.

EFI has no such fixed displacement pump that could be emptied too quickly for a low rpm engine to be capable of efficiently consuming that fuel.

regards
mech

[Miller88]

There's a warning in the owners manual on my Focus to not operate under 1250RPM with a heavy load - it can damage the dual mass flywheel. With the polyurethane dogbone mount ... I definitely don't do that - the whole car vibrates now.