Question on Tow/Haul mode

[painthorsemom]

Okay, I got to play with my new(used) '06 Silverado Dmax/Ally this weekend by hitching it up for the first time to my horse trailer. I have a 2 horse tag along with a dressing room. It weighs in at about 2800 unladen, then when I throw all my junk in the dressing room and put my horse in, it probably comes out to about 3000 lbs. I tried out the tow haul mode and it works wonders going up and down the hills around here in NE PA. It sounds like I am using up more fuel than I need to though, on the highway. Can I just use tow/haul mode on the back roads and take it off for highway travel? Would it hurt the transmission to not use tow/haul mode all the time? I am very pleased with how the truck handled the trailer. Love it!

[JohnC]

I do exactly that. I use it in the hills but not on the flats. If I was pulling 10,000 pounds I'd probably use it all the time, but on the flat the truck doesn't seem to know 5000# is hanging on the back.

[DmaxMaverick]

For "less than real heavy" loads, I suggest using T/H for starting out, then select it off once up to cruising speed. This will allow OD to engage for cruising. Once at speed and OD engaged, I engage T/H again. It should stay in OD, unless it downshifts for more power, then you'll have to select off/on again to force OD. Using this method takes advantage of the early converter lockup in T/H, and OD usage at higher (but less than T/H mode) speeds. This is also handy if your cruising speed is below 60-65 MPH, like in states where trailering speeds are limited, like CA (55 MPH). It works well, and gets the best mileage, in my experience. Early converter lockup and lower cruising engine speed is the key to fuel economy.

[painthorsemom]

Thanks for the replies! Dmax, I'm sorry, I am still a little confused by your answer. What is the coverter you are talking about and what do you mean by locking it up? Gosh, I sound like such a neophyte! Thanks for your patience! The highways around here in NE PA and NJ are rarely flat for long. I am assuming that Tow/Haul mode may not save fuel but is designed to make it safer to haul a trailer by using the transmission more for braking on the downhills? I'm so glad I joined this forum!

[DmaxMaverick]

Converter = Torque converter. The fluid coupling between the engine and transmission. It is a "lock-up" type, meaning it will lock like a manual clutch at times. In normal mode (non T/H), it will remain unlocked until about 50 MPH, and unlock when coasting at about 45 MPH. While unlocked, it is most noticeable with throttle input, as the engine speed can increase/decrease without ground speed increase/decrease (the reason auto trannies got the nickname "slushbox"). In T/H mode, lockup occurs about 18-22 MPH in 2nd gear. During this, it may feel like a "gear" engaging (drop in engine RPM), and a feeling of a solid connection between engine speed and ground speed, similar to a manual transmission. When a torque converter is unlocked, the coupling between the engine and transmission is hydraulic (centrifugal pump - like), and a lot of engine energy is lost through this fluid coupling (and the main reason ATF temps increase rapidly at lower speeds under load). Heat is expended energy. Early converter lockup minimizes this energy loss, resulting is less fuel used for a given amount of power at the drive wheels. The trade-off is, in T/H mode, shifts occur at higher engine RPM's. During empty or light load driving on flat roads, there may or may not be a gain to be had. Much depends on your overall driving habits. In any case, the more time your torque converter spends in lockup, is less heat generated by the fluid coupling.

[DickWells]

DMAX, that's exactly how I drive, while towing, with my own rig. Youl get the best of both transmission scenarios that way. Nice explanation!

[chambie]

I tried out the tow haul mode and it works wonders going up and down the hills around here in NE PA

Hello painthorsewoman,
I too live in NE PA and show in NY, NJ, OH, ect. I pull both a bumper pull and a gooseneck trailer. I always use t/h with both trailers. I may kick it off with the small trailer once i get to the main interstates and get up to speed. With the gooseneck, i leave it in t/h all the time.

[painthorsemom]

Thanks DMAX and everyone else! BTW, I made a mistake in my initial guesstimate of how much my trailer weighed loaded. It actually weighs over 4000 lbs loaded. Then you figure a heavy 2 wheel cart in the bed of the truck, with a bale of hay, etc.....
Duh, torque converter.....I should have figured that out. I have so much to learn! So DMax, it sounds like you recommend driving in T/H most of the time when hauling a trailer, to keep the transmission fluid running cooler?
Chambie, Nice Truck!

[DmaxMaverick]

I do recommend using T/H as much as is practical for you. Cooler fluid and better economy are beneficial side effects. It's new to you, so some thought will have to be dedicated to the whole process. It won't take long before it becomes second nature. Much depends on your interest, and ability, to drive your truck, rather than just ride along suggesting where it should be pointed. Many folks don't care, and just jam it in D and go. They pay a price later, of some sort. I'm in it for the long haul, and don't want to get out and push that last mile, so to speak.

[mmcm267]

Not to hijack PHM's thread but I just picked up my 07 and it has the tap shift. I am thinking after I get going in tow haul shift to manual and the TC should stay locked up in 5th and 6th? Been away from the list for a while:eek: and my new to me toy is doing well.;)