Doc279

New to the forum ! My 1990 4 runner with a V-6 automatic transmission is acting weird in over-drive. When cold it will not shift into over-drive until it has been driven 4-5 miles. Then will only shift to over-drive above 60 mph. Occasionally the over-drive will down shift back to 3rd gear while I am going downhill with my foot on the gas! Above 70 mph all is normal

Any idea's why this would be happening ? New fluid / filter etc about 2000 miles ago - I have 206,000 miles on this thing and it looks like new - the transmission is not causing any problems just annoying to me !

I get the standard 15 - 18 mpg or about 225 miles on the tank full. I have not had the codes checked - I have a manual that describes the jumper wire in the diagnostic port - but the port is not marked with letters where the jumper should be - any idea on that ? Thanks to all who will respond

Memphis4X4

Welcome to Yotatech.

First, I would recommend doing a search on "Over Drive". Several of us have had this problem and there are several posts on it. Here's one post

What is happening is the tube that carries hot coolant to the temperature sensor, which is on the upper backside of the motor, is blocked and fresh hot coolant is not circulating to the sensor. Thus, the sensor is not feeding to the ECU that the engine is at operating temp allowing the ECU to let the tranny shift into Over Drive. You will need to blow that tube out with compressed air to clear it.

When I had this done to mine, it has worked perfectly for the last 80K miles.

Again, do a search and you will get more details.
David

Doc279

I read through all of the posts and it sounds exactly like what I have been experiencing!
I could not figure out why the O/D would down shift at 60 mph
going downhill - the temperature difference at that speed NOW
makes sense. This is the greatest vehicle that I have ever owned - It will go almost anywhere at any time !

Thanks for the help !

Doc279

I read through all of the posts and it sounds exactly like what I have been experiencing!
I could not figure out why the O/D would down shift at 60 mph
going downhill - the temperature difference at that speed NOW
makes sense. This is the greatest vehicle that I have ever owned - It will go almost anywhere at any time !

Thanks for the help !

Transdude

Toyotas will not enable overdrive until there is at least some temperature in the engine.

In trans shops, when the first cold snap hits, we normally get a few vehicles in with this complaint.

Normally, a new thermostat fixes the problem, but if it is really cold out- you may just need to warm it up for a few minutes before you drive.

Provided there is no blockage, as mentioned earlier, this is part of normal operation.

-John