Auto vs manual

[anthonyca]

I know the pros and cons about drivability an auto vs manual and I have a work truck I drive daily, auto thankfully.

The truck I buy will be carying a cab over camper and towing a heavy jeep. Cab over 3500 lbs loaded and jeep and trailer 8000 lbs fully loaded.

The manual would have a new aftermarket clutch and the auto would have atleast a converter and valve body. I am not spending 5k on a tranny. I am not racing it.

When not loaded I drive fast on the freeway. I usually cruise at 80 to 85 mph. (Knock on wood.)

With 35 inch tires what would be the estimated fuel economy with an auto unloaded at 80 mph and loaded towing at 60 vs a 6speed?

What are your rpms auto vs 6 speed?

I always hear that diesels fall off a cliff for fuel economy when speeding.



Thank you.

 

[ameristar1]

The fuel economy either way will be close. It's that "I drive 85" that's going to mess the game up. A Cummins is gearing sensitive, and without knowing the gearing it will be a crapshoot at best. Here's the deal, if you drive slow and empty without the camper over 20mpg, with that camper lose another 1-3/2-4 mpg (maybe), driving 80-85 another 2-4mpg, towing another 2-4mpg. Those big tires and the extra rolling resistance, maybe 1-3 mpg.
There are calculators available online that can give cruise rpm based on gears (transmission and differential), tire size, and speed. The OD ratio should be close whether stick or manual, given the same model truck and year.

The settup you have and the way you drive is not going to win an mpg contest. The only way you can have accurate #'s is pen and paper. I'd be surprised if you got 13mpg unloaded flying along and 8-10 loaded and towing.

The other thing is whether you are running a stock unmodified truck, or if it has mods. Some of the mpg can be gained back from intake, exhaust, pump mods. The higher the power, the better the mpg, if you can keep your foot out of it.