Can low rpm damage the engine?

[KJSatz]

Well I have no idea, but to be devil's advocate...if the manual causes 15% losses and the auto causes 17% losses, that is much more than "2% less efficient." The losses are in fact (.17/.15 - 1 = .13) 13% greater.

[IndyIan]

Originally Posted by dcb

Do you have a source for this? Anytime the converter isn't locked up there are hydrodynamic losses.

This lists the automatic as %5 to %15 less efficient (not %1 to %2):
http://en.wikipedia.org/wiki/Manual_transmission#Benefits

Some automatics do lock the converter in every gear now, some don't of course. Its hard to generalize these days about transmissions, so many variations now.

Back to the original question, it would be good to have an oil pressure gauge so you could see how oil pressure varies with rpm, or even using very light oil like 0W20. Since most cars don't have one I imagine most cars are pretty safe using 1/2 throttle or less at any rpm over idle speed.
Ian

[dcb]

Fair Enough KJSats

I did learn from this discussion that aside from bucking (I think we all agree that a bucking engine is bad), there is a minimum rpm for adequate bearing oil coverage.

I do not have specific values for specific vehicles, but this diagrams the general idea:


Oil analysis and lubrication learning cennter

"This condition is represented by the equation ZN/P, where Z = viscosity, N = speed (rpm) and P = load. "

[Christ]

The numbers weren't accurate to begin with.. there is no fixed percentage of losses that can occur through a given type of drivetrain, so the numbers were placed there as holders to show the actual point - that automatic transmissions are no longer the power-defeating POS's they used to be.

I thought this would be evidenced by the use of words like "assumed" and "something like".

Sorry for not making that clear.

[dcb]

Well, folks go to great lengths for a %5-%15 improvement, so I'm not ready not rule out POS just yet

[Christ]

Remember, that drivetrain loss is frictional/heat loss... it's not linear. It's an accepted average.

In fact, the losses multiply as speed increases, almost parallel to speed.

Anyway - the point was that automatics aren't as bad as they used to be... they're nearly as efficient as manuals are. Manuals still have vehicle control and longevity in their favor though.

[Peter7307]

KiaRio ,
Welcome from me as well.
Enjoy your stay.

Cheers , Pete.

[Geonerd]

Here's a nice demonstration of the Z*N/P concept.

(Starting around 5:00)

http://www.youtube.com/watch?v=SovjQKq7NQo

[brucepick]

Very nice shots of internal parts in motion.

[RH77]

If that's the case, idling has to be murder! Especially on cold starts...

RH77