Towing in Overdrive

[Michigan-traveler]

I use OD with my Tundra and fifth wheel. I traveled from Michigan to Alaska and back last year without any problems at all. I do have the trailer package. My gauges never varied at all during the entire trip. I might add that I averaged 11.1 mpg for the entire trip. If you can pull without shifting back and forth a lot, I would use OD.

[daverain]

Automatic transmission fluid (ATF) has a life of about
100,000 miles at 175
F. At high temperatures, it oxidizes,
turns from red to brown and exhibits a burnt smell. In
addition to reducing the oil’s lubricating quality, high
temperature produces a varnish on internal parts
interfering with the operation of the transmission. Above 250F,
rubber seals harden, leading to pressure loss and
leaks. Also, the transmission can slip. In the worst cases,
clutches fail and costly repairs result.
ATF manufacturers suggest that for every 20F increase
in operating temperature above 175F, the life of the fluid
is cut in half. Hence at 195F oil life will be about 50,000
miles. Above 240F it becomes nil.

[transamz9]

A lot of people confuse OD with TC lockup. When you are running down the road and it starts to pull hard and kicks down, 90% of the time the TC is unlocking. It does that because it senses that more power is needed. This is done to let it slip per say to get the RPMs up a little. On gas motors now days it is the norm. This also happens on most trucks when you let completely off of the gas pedal and then back on. It is not kicking out of OD it is releasing the TC. Most TC won't lock up until at least 45-55 MPH depending on load. I say leave it in OD and drive it. Let the computer do it's job.

[acadianbob]

Originally Posted by daverain

Automatic transmission fluid (ATF) has a life of about
100,000 miles at 175
F. At high temperatures, it oxidizes,
turns from red to brown and exhibits a burnt smell. In
addition to reducing the oil’s lubricating quality, high
temperature produces a varnish on internal parts
interfering with the operation of the transmission. Above 250F,
rubber seals harden, leading to pressure loss and
leaks. Also, the transmission can slip. In the worst cases,
clutches fail and costly repairs result.
ATF manufacturers suggest that for every 20F increase
in operating temperature above 175F, the life of the fluid
is cut in half. Hence at 195F oil life will be about 50,000
miles. Above 240F it becomes nil.

I think there is a big difference between temporary and constant operation at these temperatures though . . .

[flyrotor]

Here is a transmission temperature chart that has been around this site a while, pretty much lays it out. If you are towing with an automatic, a transmission temperature gauge of some sort is a must! My 2005 Chevy Suburban manual stated you should not allow the transmission gauge to exceed 250 degrees, at 260 degrees it may start to reduce function to protect the transmission.

[dirttracker18]

Originally Posted by Bill_C

When the transmission is in OD, with no shifting going on, (tranny discs slip when changing gears which creates the heat) there is no heat generated in the convertor or tranny itself. It is when the engine is getting overloaded and begins to heat, it will transfer its heat to the tranny cooler, heating the tranny oil rather than cooling it.

Bill

You might be out of your range of expertise here or just misinformed. The convertor actually generates large amounts of heat as well as in the discs. Overheating a transmission is hardly ever related to an overheated engine. The heat issue is internal to the trans and not related to the dissipation in the rad. In most of our (TT owners) cases we have(or at least should have) an external trans fluid cooler and thus the issue you noted is not an issue at all.

So once again trans heat is built internal to the trans and thus critical to the issue at hand (towing in OD).

I hope that clears things up a little.

[ng2951]

Your F150 may or may not have transmission cooler. If its in the not category, you would do well to add one. A transmission cooler is lot cheaper to install install than a transmission.

You also should be monitoring your transmission temperature. If you do not have transmission temp on your panel adding a ScanGauge would be very important.

Most of the general towing advice is not to tow in OD. I would add that advice is probably even better as you approach you GCVW. I would guess the further you are away from that number the less problems you might potentially have.

[dlnw98]

Ultimately, shifting itself is what causes your transmission to wear and eventually fail. Think of it this way- every time your transmission shifts, it is one shift closer to it's last one...

If you can pull the load in OD without excessive shifting, no problem. If the transmission is shifting excessively in and out of overdrive, it's time to find a new lower gear. Take the hit on gas mileage and save the transmission. Within reason, the higher rpms the engine turns in the lower gear are irrelevant to additional engine or vehicle wear.

[transamz9]

Buy a Diesel and you won't have to worry about it.

[dlnw98]

Originally Posted by transamz9

Buy a Diesel and you won't have to worry about it.

I've got one. But that advice really wouldn't help the family trying to pull a pop-up with a Mini-van...