Towing with OD off.

[dodge man]

I always thought the tow mode wasn't really needed with just heavy load in the bed, unless you are in a lot of hills or driving a speed where the tranny is hunting gears.

 

[Diamondpilot]

Yes, 2,000# in the bed of a Tundra is only 1/5th of its rated 10,000# capacity so I would not worry about it. It would be like toting around a empty car hauler.

Chris

 

[Josh61513]

Basically it keeps you in a lower gear, by blocking the top (overdrive) gear.
There is less tendency toward "lugging".
The increase in revs for any given road speed also means the cooling fluids in both the rad and trans are pumped at a faster rate, so there is better cooling of both.

"Overdrive" is somewhat of a misnomer these days anyway, since "Top" gear is rarely a "direct" 1:1 ratio.

Tow/Haul mode is a little more complex, and different between manufacturers.
In it's simplest form it raises all the shift points, on some transmissions it also locks out the highest gear, or maybe the two highest gears.
Some just raise all the shift points and O/D doesn't come in until ~55 or above.
In others there is "intelligence" to cause downshifts if the brakes are applied but there is no significant slowing within 1/2 a second or so. Don't ride your brakes on long down grades with these, or you will have very high revs in low gears. Normal upshifting is not restored until you get on the gas again for 1/2 second or so.

Well put. "Overdrive" is simply any ratio between the engine speed and transmission output speed that is less than 1:1. Some of the higher count automatic transmissions have more than one "overdrive" gear ratios.

Another big contributor to heat generation is an unlocked torque converter. In top gear and a heavy load you will often notice that the transmission will unlock the torque converter to allow the engine to rev slightly higher where it can make more power. This works great as a short term solution, but if you are hauling a load it may stay ulocked for longer periods which can generate a lot of heat energy. If the transmission is locked out of top gear, it will not need to unlock the torque converter nearly as often because the engine is already revving higher where it can make more power.

Also, the clutch packs which are used for top gear are sometimes marginal in strength, ie GM 4L60 transmissions. When high inertia (high GCWR) shifts from 3rd into 4th are made it wears the 3-4 clutch packs significantly. This is also avoided by locking out 4th gear ("overdrive").

Using a "tow/haul" mode often influences the lockup strategy of the torque converter, another reason to use it when appropriate.

 

[KeithInSpace]

My approach is pretty simple: If the torque converter is dropping out of "lock", you need to choose a lower gear. My Expedition only has 4 speeds, so this means nearly 100% of my towing is done at over 3,000 RPM on the interstate. Oddly, I get considerably better mileage doing this than I do trying to use overdrive.

In short, if you're out of lock-up, there is nothing left to happen but for the fluid to cook.

That said, my truck doesn't have a "tow" mode, as it differs from the "O/D OFF" button. Perhaps that would help around town, but I'd still be weary on the interstate.

 

[Highbeam]

Always tow in OD unless your trans "hunts" by shifting gears and/or unlocking and relocking the torques converter. In addition, always monitor trans fluid temps with an actual gauge and not the in-dash garbage put out by the automakers.

Even with my big huge 7.3 diesel engine, I am not afraid to turn off O/D and let the rpms pick up when needed. Pretty much anything but flat interstate finds me manually engaging and disengaging O/D. There's no penalty for using the O/D button to "shift" in and out of O/D as conditions allow, just don't do it so often that you are manually hunting.

Happiness is a huge aftermarket atf cooler, a gauge to monitor temps, a nice big tractor on the trailer, a cup of coffee, and a field of tall grass that needs mowing 50 miles away.

 

[flusher]

Happiness is a huge aftermarket atf cooler, a gauge to monitor temps, a nice big tractor on the trailer, a cup of coffee, and a field of tall grass that needs mowing 50 miles away.

Yep--sounds like a little bit o' heaven.

 

[20 20]

WHAT DOES THE MANUAL SAY?

Towing a heavy load in OD will cause issues, maybe not right away but it will happen. It has a tow mode for a reason why not use it the way it is intended?

 

[dodge man]

I have a tow mode and a OD off mode on my 2007 Dodge. I think the tow mode just rasise the shift points while the OD off mode holds it out of 4th and 5th gear, but I'm not sure.

 

[firefighter jim]

When in Tow/Haul mode, should you keep gear selector in OD with a heavy load? Or 3rd? (GMC 4 speed automatic)

 

[grunewald]

I have a tow mode and a OD off mode on my 2007 Dodge. I think the tow mode just rasise the shift points while the OD off mode holds it out of 4th and 5th gear, but I'm not sure.

Have 2007.5 Dodge Diesel, 6-speed auto. Tow/haul mode upshifts faster, but still will go into overdrive. I use the manual shift, which can be set from 1 thru 6 speeds, 6 being overdrive. By setting it to 5, it will not shift past 5 gear. I'm guessing your truck is not 6-speed? Different trans.?