Transmission Overdrive Shifting Problem

I have a 1993 Mazda MPV 2WD V6 with Automatic Transmission with 116K miles. The Transmission was professionally rebuilt at 90K and a cooler was added. Everything has worked well until recently the Transmission will not shift into overdrive until it has been driven 4-6 miles. Once it warms up and shifts into overdrive it operates normally and shifts through all the ranges smoothly. I know I will probably have to take it to a professional but would like to know what to expect before I do and if there is an additive that might resolve this problem.

I have been advised that Lucas Transmission Fix might help.

Thanks for any help you can offer.

The trans has a sensor that blocks overdrive until a certain temp is reached and with adding cooler it takes longer than it did before.

Thanks hd72mm for the quick response and information. There is one thing about the cooler being the cause that is puzzeling. That is, it worked fine for over 20K before this problem started. I presume the sensor is inside and would require removing the pan?
Thanks again, your info is helpul.

No, No, No… Do not pour Lucas in your transmission. 26k on your professionally built transmission and you want to pour Lucas in it…??? This sounds like an electrical issue which needs to be checked first. It could have something to do with the temp sender or even with the TPS on the engine. If you trust the shop that did the overhaul, let them look at it to be sure.


Thanks transman618. I will definitly have that checked before doing anything else.