Automatic vs Manual - mpg difference

[eichenluft]

I'm new here so apologies if this has already been discussed. I am in the market for a new or new/used truck, Chevy Duramax Diesel - and would like to get the best mpg possible. Is there a big difference in automatic and Manual transmissions? And, how could either mpg be optimized? Thanks.

molly

[chipper]

My friendly mech tells me that the difference in the D/Max manual mileage vs auto is next to nothing. The driver will make more difference than the tranny.

[SoTxPollock]

I don't think it matters much which trans you have. Your right foot is the key.

[Craig M]

With the new 6 speed Allison on the Duramax, one gets double overdrive. For those that drive very fast on the freeways, the double overdrive auto might run the engine at a lower rpm than the manual transmission. The exact effect of rpm on mileage is difficult to determine but most think one gets better mpg at lower rpm.

[oldsnut]

With the new 6 speed Allison on the Duramax, one gets double overdrive. For those that drive very fast on the freeways, the double overdrive auto might run the engine at a lower rpm than the manual transmission. The exact effect of rpm on mileage is difficult to determine but most think one gets better mpg at lower rpm.

I agree. With my ZF6, when I was running 75-80 on the highway, rpm's were running anywhere from 24-2500. This was with everything stock, except the tires, they were 265/75r16's. From what I've heard, the double OD in the new tranny's is really nice. I would expect it to be significantly lower than 2400 rpm.

That is what kills your mileage. Your right foot and the rpms. You have a right foot that likes to go fast??? You'll pay at the pump.

FWIW though, I averaged about 17.5-18 mpg at 70-75 mph. Under 65 (OK more like 60 and below, so boooooooooooooring) I averaged just a tick under 21.

[trbankii]

Had to stop by the Toyota dealer this past weekend for some parts for my "other" truck. While there I was looking over the new FJ models and noticed that there is actually a few miles better per gallon on the automatic than the manual. Salesman came over and I was talking to him about it. Apparently the auto tranny is so controlled that it is always adjusting shift points and monitoring the engine and tranny and can squeak out better mileage that way. Watching some people I know drive stick, I think he has more than a valid point - like the kid in our office that leaves the car in fourth (for a five speed) at 65mph because "it sounds more cool" that way... :rolleyes: Of course, he could do that with an auto as well.

My only problem is what happens when you are fifty miles from a paved road and the transmission stops "thinking" for itself?

[More Power]

what happens when you are fifty miles from a paved road and the transmission stops "thinking" for itself?

IIRC 2nd gear & no more than 2000-rpm. :o

Jim