Tow/haul mode

Second Chance wrote:
What tow vehicle? Is it diesel or gas? What kind of load are you towing? Give us something to go on, here...

I my case going down a steep grade, with a diesel and a six-speed transmission, I put the transmission in "Manual" mode and select the gear I want. I can then tap the brakes as needed to supplement the engine brake.

Rob

Using tow/haul on the six speed adjusts shift points pulling weight. You can use the speed control on downhills also, set the speed you want to go down at engage the exhaust brake and sit back and enjoy the ride. It will down shift as needed and will not over rev, the ECM & TCM will not let it self destruct.

JIMNLIN wrote:


The wifes 1500 chevy 6L80e tranny has a T/H mode and does nothing but keep the tranny TC clutch open longer in 1st and 2nd while accelerating but nothing for grade braking. With the TC clutch unlocked their is no engine braking.
I use manual mode especially in the hills and do a hell of a better job than the computer anticipating best shift times (up or down).

Weird, we have a scad of those trucks and tow haul will downshift like a mofo going downhill and TC stays locked in a side by side comparison T/H vs no T/H.
I do agree though, sometimes manual mode is easier on the truck as you can keep it from "too much" engine braking on an automatic downshift.

jimbo4UT wrote:
Well you guys did answer my question. My concern was it going into first gear and destroying the engine. F350 dually pulling a TT was not the issue nor did i have a weight problem. Operator error maybe, but mostly did not the speed i was going downhill (heck i think it was 35) but on a very steep grade and i knew it would pick up more speed and it was already revving to high for my liking.

Yeah this is just another area where a experienced operator can out think the computer. The computer simply cannot anticipate best time to upshift or down shift looking down the road. The computer waits till speed changes vs experienced operator will change gears manually before that point is reached.

And not all auto trannies have a T/H mode that downshifts with brake applications or cruise control down shifting for speed control.

Generally later model diesel trannies have a much better engine braking up and down shifting/engine braking parameter than a small block gazz engine tranny.

The wifes 1500 chevy 6L80e tranny has a T/H mode and does nothing but keep the tranny TC clutch open longer in 1st and 2nd while accelerating but nothing for grade braking. With the TC clutch unlocked their is no engine braking.
I use manual mode especially in the hills and do a hell of a better job than the computer anticipating best shift times (up or down).

Don't over-think this. If you are towing any high waled trailer, or any trailer over say 3000 pounds, I recommend trans Tow/Haul mode. If you want to slow down, apply the brakes with enough pressure to get your target speed. As wing_zealot said, the downshift feature is to assist you, not take over decelerating.

I have not heard of any automatic transmissions have caused the engine to go over redline and caused damage in vehicles made in the last 20 years. The computers will simply not allow the downshift to happen under any operator inputs.

Desert Captain wrote:
Not using Tow Haul when appropriate is a great way to slowly but surely cook your transmission. If you are wise enough to have a Scan Gauge or other display of your transmission fluid temperatures you will quickly confirm the damage that is being done. Once in a while I forget to engage TH but the trans fluid display of my Scan Gauge quickly shows me the error of my ways. When I engage TH the trans temps quickly drop 12 - 15 degrees.

Most motorhome over about 27' have enough weight to warrant the use of TH 100 percent of the time. Any motorhome that is towing or loaded heavy also should always be in TH. If you are on a flat road with no headwind or a slight downhill grade turning TH off will work but why would you want to? :h

Sorry folks but the computer is smarter and more capable of getting maximum efficiency out of your coach than you are... get over it. :B On long and steep downhill grades just select a safe speed, engage both cruise control and TH and sit back and enjoy the ride. It will hold you at that speed and for most of the descent you will not burn a drop of fuel, now that is efficiency. Most of the time in so doing I never even have to touch my brakes much less hit them hard or worst case scenario ride them to the bottom but you see this behavior all of the time {those pesky brake lights give you folks away}. :S

:C

I have a readout on my dash that shows trans temps in digital. My trans hardly ever goes over 170. Normal is around 168. This is on my gas 6.4. My 12 CTD was the same way. Same trans in both. Biggest factor is ambient temps. It will run a little warmer on real hot days but the increase is the same at just a few degrees.
Maybe towing really heavy would change things. I'd be more inclined to use TH if I were towing north of 12,000 all the time.

Now my 08 F150 5.4 was a different story. The trans temps would really go up on long climbs. Seems the newer trans have much better cooling.

Not using Tow Haul when appropriate is a great way to slowly but surely cook your transmission. If you are wise enough to have a Scan Gauge or other display of your transmission fluid temperatures you will quickly confirm the damage that is being done. Once in a while I forget to engage TH but the trans fluid display of my Scan Gauge quickly shows me the error of my ways. When I engage TH the trans temps quickly drop 12 - 15 degrees.

Most motorhome over about 27' have enough weight to warrant the use of TH 100 percent of the time. Any motorhome that is towing or loaded heavy also should always be in TH. If you are on a flat road with no headwind or a slight downhill grade turning TH off will work but why would you want to? :h

Sorry folks but the computer is smarter and more capable of getting maximum efficiency out of your coach than you are... get over it. :B On long and steep downhill grades just select a safe speed, engage both cruise control and TH and sit back and enjoy the ride. It will hold you at that speed and for most of the descent you will not burn a drop of fuel, now that is efficiency. Most of the time in so doing I never even have to touch my brakes much less hit them hard or worst case scenario ride them to the bottom but you see this behavior all of the time {those pesky brake lights give you folks away}. :S

:C

Michelle.S wrote:
If the TV is anything newer the computer should protect the motor from you. So no it shouldn't down shift again unless you have a 10K redline.

Ditto.

Since the downshift to 2nd resulted in a relatively high RPM, hitting the brakes again isn't going to cause it to downshift again, until the RPMs are much lower than they currently were when the trans shifted to 2nd

Threads about tow/haul are funny.

Most mechanics I talk to say t/h will help the transmission to last longer / run cooler, some say don't worry about it.

A friend of mine drives his truck in t/h ALL the time, towing or not, to "save the transmission".

I use it whenever I am towing.

With my 2008 F250, the t/h does NOT "lockout" overdrive, just waits to shift into it until you are on a flat road for awhile. The downshifting to help in slowing sometimes kicks in more than I think is necessary, but it works great.

I have slowly come to agree with those who say to not overthink it... let the engine computer figure out the best gear. If you really don't like what the computer is doing, you can do it manually.

Edited to add: keep in mind, I am driving mostly in New England. We have hills (basically no flat spots! lol), but I really haven't driven in real mountains much.

Instead of tapping the brakes perhaps you should have hit the brakes hard the first time. Tow/Haul is not a substitute for brakes, it is a assist for brakes.

Always put it in Tow/Haul when towing or hauling. The computer will keep it from destroying itself. I have it in my MH and the Tow/Haul works amazing. With my Excursion I always manually downshifted. Now, the computer handles that and does a great job!