Towing with lifted truck

[jdonham]

I have a 2005 Chevy Silverado with the 5.3 ltr eng. I have a 6" lift with 35" tires. I am towing a StarCraft 2409 pup weighing 2476 dry. I have been told to use the tow haul mode and 3rd gear instead of tow haul and OD. Which is better and what is the difference? We live in Arizona and camping for us means heading to the mountains so I have a lot of mountain travel to look forward too. One of the trips we are planning is a 7k plus climb thru the mountains. Just concerned because my buddy has the same truck with lift and tires and pretty much the same trailer but weighs 400 lbs more (StarCraft 13rt) and he blew his tranny. Now he was doing 75-80 miles an hour on the mountain climbs and I think that helped to fry the tranny. He was using just the tow haul mode and OD.

[Kelly]

What does your owner's manual say?

I have the tow/haul mode on my Astro ... my manual says using that is most effective when your combined weight is at least 75% of your GVWR and most useful when towing a heavy trailer "... through hilly terrain", "...in low speed or stop and go traffic below 55 mph",  or when driving in parking lots.  It goes on to say "Operating in the Tow/Haul Mode when not pulling a heavy trailer will not cause damage to the vehicle, but you may experience reduced fuel economy and undesirable performance from the engine and transmission.  The Tow/Haul Mode should be used only when pulling a heavy trailer."

In the case of my rig ~ they recommend towing in 3rd.  I did use the Tow/Haul Mode in the Black Hills ... other than that I tow in 3rd.  And I can honestly say I've never remembered to put it in tow/haul when I'm in a parking lot.   :p

[flyfisherman]

I have an '02 GMC Sierra, regular cab, short wheel base with the 4.8 V-8.
Tow a small 8' box Starcraft, loaded and ready to go (with a canoe/boat on the roof of the camper), and I'm usually right around a tad over 2,000 lbs. (I've had the camper, loaded, weighed). Obviously, this is an easy tow, but a ton is a ton! Then, there is all the "junk" I carry in the truck bed! (another story)
In the flat country here along the coastal Carolina's, I usually tow in 3rd until I get out on the open road and then I'll bump it into regular OD. Moving inland toward the mountains and getting into what we call the "sand hills" ... really, just rolling hills, I'll slip the tranny into the tow/haul mode but still leaving the selector on the OD setting.  Reaching the mountains I knock off the tow/haul mode and drop down into regular 3rd and leave it there, up hill and down hill.



Fly

[fairweathercamper]

You may want to look into a tempature gauge for your transmission. Just to keep an eye on the heat built up.

You didn't mention this, but:
Another issue you may have is your tire size and your gear ratio in your rear axle. Now, I'm not familiar with your truck, but I off-road my 2005 Tacoma and I've up graded my tires from 30" stock to 32" BFG AT ko's with my 5 speed there is a difference when I shift and when I can shift into 5th gear compared to stock. With your automatic you may be working it too hard using the reccomendations from the manufacture with up-graded tire size. You may want to talk to a professional Gear installer about returning you drive train back to stock peramatures by regearing. Which isn't cheap.
Hope this helps.

[wavery]

That's correct. You have substantially changed your gear ratio with those big tires. It won't seem like a big deal because the 5.3L engine will pull it OK. However, the extra effort on the trans will generate a lot of heat. I would recommend installing the biggest tranny cooler that you can find. I would also recommend Mobile1 Synthetic Trans fluid. It disapates the heat better and improves the clutch performance under all conditions. Heat is a tranny killer.

The general rule of thumb on what mode to have your trans in is....if the trans downshifts more than once every 5 minutes, put it in a lower gear. In otherwords....if you have it in "OD" and it keeps downshifting, put it in "3rd" and keep the speed down.

Getting to your destination 10 minutes sooner isn't worth the price of a new trans. Just ask your buddy.

[Floridajeeper]

Actually your best bet is to see what your tranny does while towing it.

If it will go into OD and stay there without the torque converter unlocking and then locking a lot (this is where heat builds up) OR it doesn't try to downshift into 3rd then shift back to OD a lot (another heat builder) then you're fine in OD.

IF it does unlock the converter (you should be able to tell) or downshifts other than when passing someone or on an uphill grade then you need to downshift it and run it in 3rd....and on an uphill grade if it hunts for a gear you need to downshift.

And as stated above a temp gauge for your tranny is a GOOD thing.  If it gets hot slow down and downshift.

[wynot]

I have a 2005 Chevy Silverado with the 5.3 ltr eng. I have a 6" lift with 35" tires. I am towing a StarCraft 2409 pup weighing 2476 dry. I have been told to use the tow haul mode and 3rd gear instead of tow haul and OD. Which is better and what is the difference? We live in Arizona and camping for us means heading to the mountains so I have a lot of mountain travel to look forward too. One of the trips we are planning is a 7k plus climb thru the mountains. Just concerned because my buddy has the same truck with lift and tires and pretty much the same trailer but weighs 400 lbs more (StarCraft 13rt) and he blew his tranny. Now he was doing 75-80 miles an hour on the mountain climbs and I think that helped to fry the tranny. He was using just the tow haul mode and OD.

On my 2000 Tahoe, I rarely use Tow/Haul mode with a 3,500 lb Utah, and a 3.73 rear.  Granted, I'm not running either a lift or large tires, but I think the idea of having to use 3rd and/or tow/haul is dependent on the conditions.  We live in the eastern mountains and if the Tahoe starts hunting between 3rd and OD, then I will downshift.  Tow/Haul is primarily just a shift point delay.

[AustinBoston]

If it will go into OD and stay there without the torque converter unlocking and then locking a lot (this is where heat builds up) OR it doesn't try to downshift into 3rd then shift back to OD a lot (another heat builder) then you're fine in OD.

This is NOT the only reason to shift out of OD.  If your owner's manual says "Don't tow in Overdrive," then DON'T.  A nearly all automatic transmissions circulate less fluid through the cooler when in OD.  This is fine for normal driving.  But with some transmissions, even though they build less heat in OD, the reduced cooling in OD can cause a heat buildup problem.  There are only two reliable ways to tell:

1) The manufacturer says do/don't to tow in OD;
2) A tranny fluid temperature gauge.

Austin

[LimeJeeeep]

what was the OEM tire diameter.http://www.4lo.com/calc/geartable.htm
thats your problem.the table i have posted will give you a good idea where you were .fairweathercamper and florida jeeper off road together.in our sport ratio is everything.if the power band and wheel speed don,t work weather your crawling  on rocks or at 70 mph the tranny is going to be the hot spot....just my .02cents

[zamboni]

With my V8 2002 Explorer, I tow my Jayco 23B Hybrid in overdrive if I am on fairly level terrain where it is not shifting -- ie, more-or-less a constant speed.

However, per my manual, it says that if the vehicle is shifting in and out of OD "a lot", turn OD off.  To me, a lot, is more than once every 3-5 minutes -- or, if I see hills (or overpasses, like going through towns).

When your vehicle is running at a higher RPM, the engine as a whole is "working harder" -- this ALSO means your cooling.  Your on-board computer knows your engine is running hard, so it calls for a higher fan speed, etc.

In your case, you are fooling your on-board computer with oversized tires (is your speedometer correct???)  Unless you have had it re-calibrated, you need to personally apply the "fudge factor" to your car's needs.  That means ensuring you are not running your engine too hard at too low of an RPM.

"Forced" higher RPM's mean worse fuel economy, but better engine cooling under load.  Often, turning off "OD" also has the on-board computer bias towards more power and less economy -- letting the RPMs get higher to maximize power and cooling with less load (force) on the engine per RPM.

[Floridajeeper]

If your owner's manual says "Don't tow in Overdrive," then DON'T.  
Austin

I made the assumption this was obvious which is why I didn't include it.