We have a 95 CTD 3500 dually that does most of the towing ( 7,000+ ). Which is better? Lockout O.D. and run the engine @ 2200 RPMs at 55 mph or allow tranny to go into O.D. and cruise at 1800 RPMs. Level terrain. Does this harm the engine to save the tranny ? Owners manual says to lock-out O.D only in mountainous regions when tranny is shifting in and out of O.D due to slower speeds. Please help settle a long standing discussion! Thanks, Vicky

 

On flat ground with that load the only thing you'll hurt is the fuel economy if you lock out OD. The engine doesn't care one way or another, and the weight and terreain won't hurt the trans. Do what keeps the peace.

 

When I'm towing, I just keep my rpm's above 1500, as long as the tranny isn't hunting. I towed a 12,000 lb. fiver from Florida to Michigan right up I-75 and never had to shift out of OD.

DeWain

 

Vicky,
I also use the OD most of the time. You will learn the more you tow when the truck wants to shift and can throtle up or down as needed. As long as your trans is not hunting for gears and you are traveling 55+ mph the trans is happy in OD.
Get a trans temp gauge and keep an eye on temps.

 

Mike6256 is right on. Get the trans guage , you won't be sorry.

 

Hi Vicky, welcome to DTR! You can learn a lot here and everyone is very helpful.

I have a 95 3500 also. Before I turned it up it would kick in and out of OD pulling my TT (loaded 12,000+) so I had to run it with the OD off. Since I tweaked it, I run in OD all the time no problem.
Like the guys said, get a Trans gauge to monitor your temperature.