Overdrive problems

[randyman]

I have a 91 runner and have had problems with it not going into O.D. until 30 minutes of driving (highway) even after 15 minutes of warm up. It is getting real cold here in NE and the cold makes it worse. I have a brand new 190 thermostat and the trans shop says that it checks out good. Could it be the temp switch? Isn't it supposed to shift at 130 degrees? The truck is at full operating temp according to the guage as well. Any help would be a blessing.
Randyman (rookie)

 

[boston_kevin]

Not sure about a '91, but I think the shifting temp is based on tranny temp, not engine temp. Anyway you can get a tranny temp gauge on that?

 

[randyman]

Even still, the temp was well over the 130 mark from warm up and drive time. I was under the impression that the temp switch sends a signal to the ECM telling the trans to shift into OD. It's frustrating driving my 50 minute commute doing 50mph in a 65 zone and being passed by senior citizens in wheel chairs...: Thanks, I don't think a trans temp guage would help though.
Randyman

 

[boston_kevin]

You might consider adding a block off plate (piece of cardboard) in front of the radiator to warm things up a little faster. That may help to decrease the amount of time it needs to reach that critical shift point. Start by blocking off 1/3 of the radiator and watch your engine temp.

 

[randyman]

Thanks Kevin, already done that. Still no help.

Randyman

 

[toto]

boston_kevin is correct - the trans fluid has to warm up to a certain temperature before it will shift into overdrive. Engine temp is irrelevant, but of course driving will warm up both the engine and the trans.

This is a feature of all Toyota products.

 

[randyman]

Thanks toto, I am aware of that since I have owned many Toyota products. The problem is that it is warmed up for 15 minutes and then 30 minutes drive time and still no OD.
Randyman

 

[toto]

randyman, you intrigued me enough to get the book out, and I learned something!

It turns out I'm wrong about the engine temp being irrelevant - it does matter! The minimum thresholds seem to be very dependent on your powertrain. I've owned Toyotas for years, and their behavior certainly makes it seem like the trans fluid temp is the only thing that matters.

I don't have service manual pages going back to 1991, but here's what I did learn:

- On the 3.3L V6 powertrain used in some 2004-2006 Toyota/Lexus models, the overdrive won't kick in unless the ATF is at 28 degrees F (yes, that's 28 - it's not a typo unless the book is wrong) _and_ the engine coolant is at 154 degrees F and you're moving at least 43 mph.

- On the 3.4L V6 powertrain used in 3rd Gen 4Runners and Tacomas, the overdrive won't kick in unless the engine coolant is at 140 degrees F. It doesn't mention the ATF temp as being a factor, although it does say that "normal" temp for the ATF is 122-176 degrees F.

I'm not sure how much that helps you, other than the fact that the engine temp does matter. Maybe that's another direction to check into.

 

[randyman]

The engine temp thing is why I may replace the temp sensor that reports to the ECM. I have put in a new thermostat, placed cardboard in front of the radiator (which is also new) and the temp sensor for the ECM is the only thing that hasn't been replaced....except the solenoids in the tranny but we won't go there unless we have to.$$$$$
Thanks for looking into it for me, the input here has been good. Have a Merry Christmas and God bless this new year. I will let you know what I find out.

Randyman