Drive VS. OD gas mileage on hwy ?

[fisher1648]

I pull a medium sized trailer (14ft single axle with about 1200 lbs of stuff) on the hwy often. Unfortunately, I have been doing this with the trans (700R4) in OD rather than Drive - my bad. It's likely the cause of my recent tranny failure.

I'll now be pulling with the tranny in Drive

My question is should I expect a dramatic gas consumption increase ? Seems the higher RPMs are going to consume more gas.

Any thoughts ?

 

[rjfguitar]

It all depends on the rest of the truck. If the truck was geared to pull loads and the tranny was fresh it should be able to pull only an extra 1400lbs in OD.

You shouldn't see much more than a few MPG drop off in drive. In some cases if the truck is geared way to high running in drive will cost very little if any loss of mileage.

 

[fisher1648]

It's a 1987, 350 TBI engine, 33X12.5 tires, 4:10 gears......

At what trailer weight do they recommend pulling in Drive rather than OD ??

Thanks, Eric

 

[tarussell]

Just an opinion - I would let the mileage fall where it may and save the strain on the tranny and use drive while towing. Don't let the tranny hunt for the right gear or battle between lock-up in the converter .

If in doubt put it in drive - your TH700R4 will thank you for it .
Tom

 

[fisher1648]

OK- thanks...sounds like Drive it is.

 

[MarcS]

Also put in a trans cooler, they're pretty cheap, easy to install and will
help the trans last alot longer.

 

[84_Chevy_K10]

Higher RPMs do NOT automatically cause more fuel consumption. That is a total myth. Fuel consumption is based on engine load. Your engine will work much harder trying to pull your under geared truck + your trailer with those big tires. Keep it in drive all the time and it will pull much better.

If high RPM causes crappy fuel mileage, my 1 ton truck with 30.5" tires, 4.10 gears, and no overdrive would never get 14 MPG on the highway unloaded--but it does.