Hi guys
so i saw a post the other day talking about towing with tow mode off .
so yesterday i towed my jayco camper from se Ky to washington Dc.camper is about 9500 lbs the trip went well except the traffic in Dc killed me lol.my question is why use tow mode.for those of you that dont know here is some nice hills between here and there and the truck did great.the max eot was 231 and ect 224 going up the steepest hills with tft not higher than 179 regurlay the tremps werre normal eot 217 ect 208 tft 269 os so.i also got better mileage. checking it by hand i got 9,3 mpg and i was traveling 65 to 70 most of the time.
Why use tow mode?

 

Tow/Haul changes the shift points and raises the RPM's, lowers the strain and heat build up in the transmission. Down hill it will provide grade braking. Your choice as when or if you use it.

 

It helps hold gears when in rolling hills so the trans isn't shifting and it is a big help in slowing down without tearing up the brakes.

 

I've noticed a change in fan operation. Not sure, but will be doing some testing next week. Will be towing a ways, and mostly level ground.

 

I seldom use the tow haul unless I am pulling 300 to 600 bushels of grain with my truck. That is a HECK of a load so I use it then, but just pulling my boat I seldom use it unless in a very hilly area.

 

pulling our 13k pound trailer i can't even imagine having to stop without tow haul on... Matts 8k tow tune with tow haul on provides wicked engine braking and i just feel added safety knowing i'll be able to stop in time... makes a difference. I'll turn it off when i know i wont be needing to stop anytime soon.

 

I like tow/haul mode in stop and go and around town. There's a little bit of engine braking so it slows quicker when lifting off the throttle, and the shifts are delayed a little so it accelerates with a little less strain. It's pretty cool to not be the hold up in traffic when towing a pretty bif fifth wheel. Once on the open road I flip it off so that it shifts into overdrive quicker. Generally, I'm speeding up at a slower rate when already rolling at 55 or better. And I don't want engine breaking at these speeds either, if I gain 5 or 10mph going down a hill it's bonus energy. For me though, ther comes a time when the hills get big enough and long enough I'll flip it back on and slow down. Just seems to make life easier for the truck. I decide when to go back to tow haul mode by watching EOT. Basically, 235deg and it's time to ease up.

 

By "engine braking", do you mean how the tranny kinda shifts a little sooner during deceleration to put a little extra load on the engine, rather than the brakes?

It's not like a jake brake is it? I assume not...just checking!

 

Yea, downshifts sooner and slows the truck. I've also read something about the turbo acting different to help but I'm not sure if that happens also. I think a "Jake" changes the valve timing, leaving the exhaust closed longer to use the compression in the cylinder to slow the truck.

 

I also read that tow haul shifts the vanes in the turbo to provide more braking, but I'm not sure if thats true or not.

I like to use it in stop and go traffic too, most of the time I don't have to use the brake, I can just lift the throttle to slow down and add throttle to move forward.

 

I tow a 10,000lb 5th wheel and I always us tow/haul except when I am a HW speeds with very light hills.

Robert, towing 9,XXXlbs I strongly suggest using tow/haul. It decreases allot of strain on the engine and transmission. With stock tuning, 5th gears loves to shift early. This creates allot of excess heat(waisted energy) and ware on the transmission while towing.

 

You can with custom programming have the turbo create back pressure in order to help with braking as well. In stock form though, as far as I know, everything is done with the tranny to create the extra load on the engine to help slow the truck down. Same thing on my 150 as well, but far far less aggressive.

 

If its all done within the transmission, how come you can be cruising at, say, 1700 rpms, turn tow haul on, and as soon as you lift you are still at 1700 rpm but it slows you down much quicker? Is that because normally the torque converter lets the truck free wheel and with tow haul on, it locks it up to use the engine compression to slow the truck like in a manual?

 

No, it's not the torque converter. You get engine braking with the torque converter locked or unlocked. It's the turbo.

When coasting with tow/haul on the turbo vanes are closed to create backpressure on the engine which causes drag, hence the engine braking. The transmission leaves the torque converter unlocked but will downshift to a lower gear.

 

I guess Mark cleared up any doubts on the subject.