Towing with Overdrive On

[cdalton]

Somebody please educate me; is it hard on a tranny to tow in overdrive? I have an '03 Tundra V8 4x4 with the towing package. The truck has enough torque to tow my 23' boat in overdrive without needing to downshift much (live in Indiana...not many hills). I am usually running about 65 mph so if I shut the overdrive off it seems like the engine is revving too high for an extended period of time; gas mileage I am not so concerned about, I am mainly concerned with prolonging engine and transmission life.

[akauth]

Originally Posted by cdalton

Somebody please educate me; is it hard on a tranny to tow in overdrive? I have an '03 Tundra V8 4x4 with the towing package. The truck has enough torque to tow my 23' boat in overdrive without needing to downshift much (live in Indiana...not many hills). I am usually running about 65 mph so if I shut the overdrive off it seems like the engine is revving too high for an extended period of time; gas mileage I am not so concerned about, I am mainly concerned with prolonging engine and transmission life.

Don't tow in overdrive. You can get away a couple of times but don't do it regularly. The downside is worth the savings.

It will be fine to have the extra rpms. You'll be trading engine life for transmission life, but the latter is going to hit you much sooner. Towing in overdrive is a bit hard on the planetary gears. Often times it's as simple as a bearing or bushing that gives out and then everything else is hosed.......



Alan

[KLS]

Those extra rpms don't shorten engine life. The engine is running faster but easier. It is not the same thing as comparing full throttle 2000 rpm to full throttle 3000 rpm. It is more like comparing 40% throttle 2000 rpm to 25% throttle 3000 rpm (I just pulled those throttle numbers out of thin air, but I hope you get the idea).


Ken

[dyogim]

Leave it off when towing.

[akauth]

Oh, one other thing....

The only *real* downside to turning off overdrive (other than burning more gas) is really that the trans fluid is going to get hotter than if you had it on as you'll have more viscous slip (energy) that's absorbed by the fluid (in the form of temperature).

So it's best if you have an aux trans cooler installed if you don't already have one installed OEM.

Other than that, don't sweat turning off the overdrive.

Alan

[HBjeff]

i tow my 2 quads on their little trailer in OD when its flat ground. it never kicks up and down so thats not too bad. total wieght is under 1500 lbs.

[RockyMtnRay]

Originally Posted by cdalton

Somebody please educate me; is it hard on a tranny to tow in overdrive? I have an '03 Tundra V8 4x4 with the towing package. The truck has enough torque to tow my 23' boat in overdrive without needing to downshift much (live in Indiana...not many hills). I am usually running about 65 mph so if I shut the overdrive off it seems like the engine is revving too high for an extended period of time; gas mileage I am not so concerned about, I am mainly concerned with prolonging engine and transmission life.

As long as the transmission isn't downshifting to 3rd very much, or more importantly, the torque converter clutch isn't unlocking very frequently, IMO both engine and transmission life on an '03 or newer Tundra is unlikely to be affected much one way or another if you do or do not tow with OD on.

The mentions above about planetary gear weakness are applicable only to the '00-'02 models...begining with the '03 models, Toyota changed key internals of the transmission (in particular certain thrust washers) which apparently totally solved that problem. I can not recall a single report here at TS.COM of a planetary gear failure on a '03 model...not one...though there have been many, many reports of such failures on the pre-'03 models.

I have an '03 which I regularly use to tow a 4000 lb travel trailer across the Colorado mountains. I equipped the truck with a pan mounted transmission temperature gauge which I monitor very closely while towing. I discovered last year that the transmission temperature was often 5 to 10 degrees cooler, yes cooler, if I towed with OD on as long as the road was flat enough that the transmission torque converter clutch stayed locked up most of the time. Certainly if using OD caused the TC clutch to frequently unlock...or the transmission to frequently downshift...then the resulting fluid slippage definitely would increase the transmission temperature. But as long as the TC clutch was staying locked in OD..and engine RPMs were lower...then the trans temp was typically a few degrees cooler than if I had OD turned off and let the truck run in 3rd gear (also with the TC clutch locked).

When the TC clutch is locked, there is no fluid slippage and therefore the primary control of transmission temperature is the coolant temperature in the bottom of the radiator. My suspicion is that higher engine RPMs from turning OD off were causing the coolant in the bottom of the radiator to be a bit warmer, hence the transmission pan temperature was also a bit warmer.

I also noted that my towing gas mileage averaged about 1 mpg higher when I mostly could tow with OD on versus with OD off. And in-cab engine noise is about 5 db lower (i.e. quite noticeably less) when towing with OD on.

After considering all of the above, I've concluded that as long as TC unlock/transmission downshifting in OD are infrequent, then transmission/engine life on an '03 will not be adversely affected by towing with OD on. I've also concluded that towing with OD on will noticeably improve gas mileage and will definitely reduce engine noise coming into the cab. So I'm personally going to tow with OD on whenever the road grades allow me to do so without frequent TC unlock or downshifting.

For '00-'02 Tundra owners: Please note that my conclusions pertain strictly to the '03 and newer models...for an '02 or earlier, the known weakness of the planetary gearset definitely suggests not using OD when towing with these model years.

[akauth]

It's pretty certain that if you turn the overdrive off vs running with it on that the transmission fluid is going to run hotter. That energy that is being absorbed through the torque converter has to go somewhere. It can only come out in the form of heat. Once the trans hits proper temp that has to go out through the radiator/aux cooler.

In fact, the trans engineers use the same principal to help heat up the trans fluid to operating temp when it's cold. They'll keep it out of overdrive so that both the radiator and the torque converter slip will help heat the fluid. The slip causes causes a conversion of mechanical energy to heat energy which has to be absorbed by the fluid. Once the fluid hits proper operating temp, the slip is eliminated and the converter can lock up properly.

If fact, if you put too large an auxilary cooler on a vehicle it's possible that in thinking "some is good, more is better" one ends up creating a situation during wintertime where the fluid gets cooled too much and overdrive is bypassed to keep heating up the fluid. The converter keeps slipping to heat the fluid and the aux cooler keeps taking too much of the heat away. It's especially easy to do this if you blow a trans and decide to put in an aux cooler as your primary cooler instead of replacing or flushing (flushing is not to manufacturer spec but it often is fine) the OEM radiator. This causes a problem because the OEM radiator heats the fluid when it's cold and cools the fluid once it get too hot. But an aux cooler has no real interchange with the radiator coolant so it's very inefficient for a souce of heat even if it's behind the radiator. It can't heat the fluid, it can only cool it.

The problem that is going to show up by having it in overdrive while towing is higher mechanical pressures. The big question: are those higher pressures enough to cause excessive wear. Often it's a small part failure that causes the whole works to get ruined since it's an all or none proposition.

The guys who would be the last voice on whether to put it in overdrive or not would be the guys who rebuild transmissions. They'll be able to tell what the real world results are vs. what the engineers intended since they'll see the failures. Other than that it's purely hypothesis - even if you do keep it within manufacturer suggestions. Doen't mean the OEM design wasn't screwed up.

One thing that will kill a trans faster than anything is excessive heat though so that has to be taken into account when towing. High heat dramatically shortens a transmissions life prematurely.

Alan

Originally Posted by RockyMtnRay

As long as the transmission isn't downshifting to 3rd very much, or more importantly, the torque converter clutch isn't unlocking very frequently, IMO both engine and transmission life on an '03 or newer Tundra is unlikely to be affected much one way or another if you do or do not tow with OD on.

The mentions above about planetary gear weakness are applicable only to the '00-'02 models...begining with the '03 models, Toyota changed key internals of the transmission (in particular certain thrust washers) which apparently totally solved that problem. I can not recall a single report here at TS.COM of a planetary gear failure on a '03 model...not one...though there have been many, many reports of such failures on the pre-'03 models.

I have an '03 which I regularly use to tow a 4000 lb travel trailer across the Colorado mountains. I equipped the truck with a pan mounted transmission temperature gauge which I monitor very closely while towing. I discovered last year that the transmission temperature was often 5 to 10 degrees cooler, yes cooler, if I towed with OD on as long as the road was flat enough that the transmission torque converter clutch stayed locked up most of the time. Certainly if using OD caused the TC clutch to frequently unlock...or the transmission to frequently downshift...then the resulting fluid slippage definitely would increase the transmission temperature. But as long as the TC clutch was staying locked in OD..and engine RPMs were lower...then the trans temp was typically a few degrees cooler than if I had OD turned off and let the truck run in 3rd gear (also with the TC clutch locked).

When the TC clutch is locked, there is no fluid slippage and therefore the primary control of transmission temperature is the coolant temperature in the bottom of the radiator. My suspicion is that higher engine RPMs from turning OD off were causing the coolant in the bottom of the radiator to be a bit warmer, hence the transmission pan temperature was also a bit warmer.

I also noted that my towing gas mileage averaged about 1 mpg higher when I mostly could tow with OD on versus with OD off. And in-cab engine noise is about 5 db lower (i.e. quite noticeably less) when towing with OD on.

After considering all of the above, I've concluded that as long as TC unlock/transmission downshifting in OD are infrequent, then transmission/engine life on an '03 will not be adversely affected by towing with OD on. I've also concluded that towing with OD on will noticeably improve gas mileage and will definitely reduce engine noise coming into the cab. So I'm personally going to tow with OD on whenever the road grades allow me to do so without frequent TC unlock or downshifting.

For '00-'02 Tundra owners: Please note that my conclusions pertain strictly to the '03 and newer models...for an '02 or earlier, the known weakness of the planetary gearset definitely suggests not using OD when towing with these model years.

[lelandstanford]

Originally Posted by akauth

It's pretty certain that if you turn the overdrive off vs running with it on that the transmission fluid is going to run hotter. That energy that is being absorbed through the torque converter has to go somewhere. It can only come out in the form of heat. Once the trans hits proper temp that has to go out through the radiator/aux cooler.

In fact, the trans engineers use the same principal to help heat up the trans fluid to operating temp when it's cold. They'll keep it out of overdrive so that both the radiator and the torque converter slip will help heat the fluid. The slip causes causes a conversion of mechanical energy to heat energy which has to be absorbed by the fluid. Once the fluid hits proper operating temp, the slip is eliminated and the converter can lock up properly.

If fact, if you put too large an auxilary cooler on a vehicle it's possible that in thinking "some is good, more is better" one ends up creating a situation during wintertime where the fluid gets cooled too much and overdrive is bypassed to keep heating up the fluid. The converter keeps slipping to heat the fluid and the aux cooler keeps taking too much of the heat away. It's especially easy to do this if you blow a trans and decide to put in an aux cooler as your primary cooler instead of replacing or flushing (flushing is not to manufacturer spec but it often is fine) the OEM radiator. This causes a problem because the OEM radiator heats the fluid when it's cold and cools the fluid once it get too hot. But an aux cooler has no real interchange with the radiator coolant so it's very inefficient for a souce of heat even if it's behind the radiator. It can't heat the fluid, it can only cool it.

The problem that is going to show up by having it in overdrive while towing is higher mechanical pressures. The big question: are those higher pressures enough to cause excessive wear. Often it's a small part failure that causes the whole works to get ruined since it's an all or none proposition.

The guys who would be the last voice on whether to put it in overdrive or not would be the guys who rebuild transmissions. They'll be able to tell what the real world results are vs. what the engineers intended since they'll see the failures. Other than that it's purely hypothesis - even if you do keep it within manufacturer suggestions. Doen't mean the OEM design wasn't screwed up.

One thing that will kill a trans faster than anything is excessive heat though so that has to be taken into account when towing. High heat dramatically shortens a transmissions life prematurely.

Alan

It's my understanding that for A340 in "OD on" mode the shift pattern is 1-2-3-4-4L and "OD off" mode is 1-2-3-3L.

So either way, once you reach freeway speed. The TC is going to be locked. The only diference is engine and transmission internal RPM. More heat will be produced in the transmission but nothing like TC slipperage.

[mustang67408]

Originally Posted by lelandstanford

It's my understanding that for A340 in "OD on" mode the shift pattern is 1-2-3-4-4L and "OD off" mode is 1-2-3-3L.

So either way, once you reach freeway speed. The TC is going to be locked. The only diference is engine and transmission internal RPM. More heat will be produced in the transmission but nothing like TC slipperage.

Lock-up point
D position V-8
(2UZ-FE / A340E & 340F)
(Throttle valve opening 5%)
LOCK UP ON = 71 - 78 km/h (42 - 46 mph)
LOCK UP OFF = 64 - 71 km/h (37 - 42 mph)

Lock-up point
D position V-6
(5VZ-FE / A340E & 340F)
(Throttle valve opening 5%)
Lock-up ON = 71-78 km/h (44-49 mph)
Lock-up OFF= 64-71 km/h (40-44 mph)

[akauth]

Since I don't rebuild them and I don't even come close to tearing them down I called Ron's Transmission in Sunnyvale which is one of the premier trans builders in our area. When I have something done, I'll go to them since they're the one even the dealers refer people too (and there are close to 200 trans rebuilders in a 25 mile radius here). They'll rebuild to OEM (plus) standards so you're going to have the strongest trans possible when you get it back which is even better than the dealers remanufactured (I know they call them new) transmission.

I had asked them what they recommended for usage.

Basically the breakpoint is about 1,000 pounds for a load. Any more leave it off, any less go ahead and turn it on.

But even then, his comment's were towing with those transmissions with overdrive on was a bit "iffy".

It's better to tow one gear down from overdrive to minimize planetary involvement while towing. Makes sense to me because like anything - the less parts involved the less chance for one of them failing. (KISS principle)


Alan

[mustang67408]

Originally Posted by KLS

Those extra rpms don't shorten engine life. The engine is running faster but easier. It is not the same thing as comparing full throttle 2000 rpm to full throttle 3000 rpm. It is more like comparing 40% throttle 2000 rpm to 25% throttle 3000 rpm (I just pulled those throttle numbers out of thin air, but I hope you get the idea).


Ken

Ken is 100% correct, your not going to hurt the engine.
I have towed over 600 miles to and from Las Vegas to South Calif and back in 3rd gear at 80 mph@ 3800 rpm or so w/33" tires and 4.56 gears. The vacuum gauge read 10 inches of vac most of the way, which is the load off the engine and your using the gears to move the vehicle. The engine never missed a beat and I was never worried about it. You shouldnt drive that fast when towing, but I wanted to know if I could do it, if I had to.

[akauth]

Originally Posted by mustang67408

....You shouldnt drive that fast when towing, but I wanted to know if I could do it, if I had to.

Yeah, right...... (I wonder if the CHP would buy that....)

[mustang67408]

Originally Posted by akauth

Yeah, right...... (I wonder if the CHP would buy that....)

The CHP would back down when I tell him I am a member of TS!

[akauth]

Originally Posted by mustang67408

The CHP would back down when I tell him I am a member of TS!

Just in case that doesn't work you might want to run into a local costco. I just got back from our local one and I see they've got a whistler radar detector for sale there for $124 dollars.

Last time I got a ticket (it's been a while) that was less than the cost of the fine plus traffic school. I might pick one up just for the heck of it.

Whistlers usually been the best over the years. Don't know if they still are. Actually, I think thats escort that's been the best. But Whistler $199 detector is only $124 at costco.


Alan