Gmc/Chevy tow/haul question.

[Bigdomino]

I have 2017 gmc with 6.2 engine and 8 speed trans. I have not towed yet. Just got my TT. I am wondering how well the tow/haul function works? How happy are with the function? Steve

[JeremiahM]

I haven't driven your particular truck, but it is definitely to the benefit of you and your vehicle to utilize that function. It's safer, and cuts down on the wear and tear on the vehicle by being programmed to keep it at it's optimal state for a towing circumstance. Transmission will run cooler, and brakes will last a lot longer from utilizing the engine braking feature

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[FishAr]

Originally Posted by Bigdomino

I have 2017 gmc with 6.2 engine and 8 speed trans. I have not towed yet. Just got my TT. I am wondering how well the tow/haul function works? How happy are with the function? Steve

Worked great on my 2008, 2013, 2015 colorado, 2015 silverado 1500, and works great on my 2015 2500hd.

[motorbreath]

I have the 6 speed, tow/haul works great except that it downshifts if you tap the brakes. I have had it downshift almost to redline until I figured out that it was responding to brake input.

Originally Posted by Bigdomino

I have 2017 gmc with 6.2 engine and 8 speed trans. I have not towed yet. Just got my TT. I am wondering how well the tow/haul function works? How happy are with the function? Steve

[Rustic Eagle]

Originally Posted by Bigdomino

snip....... I am wondering how well the tow/haul function works? How happy are with the function? Steve

With both my prior and present GM 2500HD's I always engaged the tow/haul mode when I tow my TT....., definitely enhances a TV's towing characteristics when towing moderate to heavy trailers.

https://www.youtube.com/watch?v=424R6OyfdH8

Bob

[01tundra]

I've found that in our particular case we get better fuel mileage while not using tow haul (6.6L DM). Our TT is so light that putting the truck in T/H mode makes it stay in 5th too much.

The manual says only use T/H if you're at or above 75% of your GCWR:

"Tow/haul is designed to be most effective when the vehicle and trailer combined weight is at least 75% of the vehicle's gross combined weight rating. Operating T/H when lightly loaded or with no trailer at all will not cause damage. However, there is no benefit to the selection of T/H when vehicle is unloaded. Such a selection when unloaded may result in unpleasant engine and transmission driving characteristics and reduce fuel economy."

In our case 75% of GCWR would be 18,975 lbs and we're only at 12,400 lbs fully loaded.

I've tried it both ways and have seen approximately 2 MPG increase in average with T/H turned off.

[Ruth]

We have the tow function on our 2007 Chevy 2500HD and we are very happy with it. We currently tow a 34ft. TT and tows quite well. It changes the shifting of gears slightly and also works as a brake when going down steep hills. As we camp in NH, we have the White Mountains to contend with. We never paid attention to mpg, but I believe we do get better mpg with than without using it.

[sennister]

Originally Posted by motorbreath

I have the 6 speed, tow/haul works great except that it downshifts if you tap the brakes. I have had it downshift almost to redline until I figured out that it was responding to brake input.

I have the 6L80 in my Denali with the 6.2. I agree that it will downshift when tapping the brakes. I haven't had any issues where it ever got close to redline though unless I tried to take over manually with the +/- rocker on the shift lever. The reason for the downshifting is to do some engine braking to help with slowing so less brake effort is needed. Brakes convert kinetic energy into heat which is dissipated through the rotors. The more heat built up in your brakes the less stopping ability you have and your braking distance increases. So engine braking is a good thing.

I will agree with others in that it will increase fuel consumption but that isn't really something one can avoid pulling a camper. The main thing it does is change the shift point. It will try and hold gears longer as well as downshift to provide some engine braking effect as mentioned above. The reason for holding gears longer is so that it does less shifting. When going through shifts you are going to heat up the transmission more. So if the truck is constantly hunting for a gear while pulling a heavy load you will see transmission temps rise. You can combat this by using the tow/haul mode or by manually shifting.

[SEAHAWKS_12]

I have also had the issue of the truck shifting to redline while hitting the brakes. Generally I put my truck in T/H mode but I will use the "manual" shifter to have better control of the transmission. Hills especially. The more shifting that's happening, the more heat your transmission builds. If you are on long flat freeway T/H might not be necessary and you could increase your mileage as others have said. That being said, I have not drove the 8 speed so it could be completely different and they could have fine tuned the shift points and "engine braking". Check out www.silveradosierra.com there are a lot of threads about T/H mode and probably threads about your specific truck.

[rwk5159]

Some excellent points made here.

I personally do not use Tow/Haul mode. (I'm under 75% GCWR)

I only upshift manually.

I downshift with the right pedal. My foot finds that sweet spot and knows how much grade I can pull and how much throttle to get the transmission to downshift. When it downshifts up a grade, I use the upshift/downshift selector to match the gear I'm actually in, then manually upshift when I feel the engine come off load.

When I need engine braking, I downshift manually.

The engineers at GM (and others) spend too much time behind the desk. Driving isn't and electrical phenomenon...it's the link between the body and the mechanics, Kemosabe. (I can comfortably say that...I'm an electrical engineer)

Using this method, I'm able to keep transmission temps below those of using Tow/Haul mode by around 20 degrees on the highway. (City temps stay the same). Remember, transmission temps rise from both shifting AND the amount of force applied against the transmission. (ie. 5000 RPMS CAN generate more heat than 3000 RPMS, not because of rotation, but because the power output of the engine at 5000 RPMs is greater.)

[JeremiahM]

Originally Posted by rwk5159

Some excellent points made here.

I personally do not use Tow/Haul mode. (I'm under 75% GCWR)

I only upshift manually.

I downshift with the right pedal. My foot finds that sweet spot and knows how much grade I can pull and how much throttle to get the transmission to downshift. When it downshifts up a grade, I use the upshift/downshift selector to match the gear I'm actually in, then manually upshift when I feel the engine come off load.

When I need engine braking, I downshift manually.

The engineers at GM (and others) spend too much time behind the desk. Driving isn't and electrical phenomenon...it's the link between the body and the mechanics, Kemosabe. (I can comfortably say that...I'm an electrical engineer)

Using this method, I'm able to keep transmission temps below those of using Tow/Haul mode by around 20 degrees on the highway. (City temps stay the same). Remember, transmission temps rise from both shifting AND the amount of force applied against the transmission. (ie. 5000 RPMS CAN generate more heat than 3000 RPMS, not because of rotation, but because the power output of the engine at 5000 RPMs is greater.)

Yes and no, more rpms also means the transmission pumps spinning faster therefore keeping the fluid circulating better through the system, lock a transmission in OD while not going fast enough (towing heavy) and you'll also see a lot of heat generated... back and forth shifting, definitely generate a lot of heat though

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[redenbacher]

I've also (as was noted earlier) that staying out of tow/haul gives me better gas mileage. In addition to the weight of the trailer, I think a lot has to do where you do your driving. Much of my driving is across very flat terrain. If I am going into more hilly terrain, I switch to T/H.

[mohok1]

IMHO, I think the best source of information is in your owners manual. After getting my 2008 Chevy Duramax 6.6 V8, 6 speed Transmission, I got the truck in 2012, it took me a while to get comfortable with T/H mode. After 60 or so MPH it shifts into 6th gear anyway. T/H does change the shift points to handle the load and is designed to protect the transmission. MPG change is not that noticeable, your right foot has a lot to do with MPG. This is disputable, of course.