I've read in a few places about folks using Tow/Haul mode to cool their trannies down. Can someone explain how this works?


And speaking of tow/haul mode, I'd like another clarification. When hauling or towing a heavy load, I understand how gear ratio and compression help us slow our vehicles. On this basis, the downshifting initiated by tow/haul makes perfect sense to me.


When trying to accelerate with a heavy load, we want the maximum power/torque output to assist us. In a gasser, which redlines at 5,000 rpms or greater, the power band is generally higher up in the revs. On this basis, the tow/haul mode, which keeps you in the same gear longer than your vehicle otherwise would, this makes sense (keep the revs higher where all the power is).


Our diesels, however, generate peak power much lower in the rev range--1,800 is it? How does signaling my tranny to upshift at 2,500 help me accelerate/tow better? Or is my diesel engine trapped in a gasser chassis designed with gasser features?


Thanks,


Terel

Tow/haul will reduce some of the heat buildup over regular mode because it locks the torque converter in 2,3,4 and 5 versus regular mode which only locks up in 5. By locking the converter sooner, there is less fluid slippage in the lower gears which will reduce heat buildup. It also changes the shift points in the lower gears to "hold" longer before upshift to assist in pulling heavy loads up to speed. The trans braking is not really "compression" braking - it recirculates fluid in the trans to produce drag. If using tow/haul for braking assistance on a long downhill with load, it will heat up the tranny (by saving your wheel brakes). Tow haul and regular modes are seriously programmed for the diesel engine - just two modes of operation based upon intended use. Tow/haul is rarely required if not loaded. I do use mine in serious stop-and-go situations to keep the tranny cool and save the amount of throttle/brake - throttle/brake required.