I was towing my car with my trailer this Sunday in 100 degree temperature and had my O/D off light start flashing shortly after starting off. When I arrived at the track and pulled into the drivway there second gear would just rev up high and then go into 3rd gear. Comimg home several hours later the O/D off light started to flash again.

The next day after unhooking the trailer and driving the truck around every time it shifts into 2nd the motor will rev up then settle down. I did pull a code saying the transmission had over heated. Does this sound like the transmission is damaged?

I have a 2000 4.6 2wd expedition and the combined weight of the car and trailer is about 6000 lbs.

 

If that's a 4R70W in the Expy-you've probably got a sticking accumulator piston,or possibly have hurt the intermediate clutch. I'd say the clutch is pretty difficult to hurt-unless that accumulator is sticking, so it may be a combination of both...one causing the other.
JL

 

The wifes (2003 2wd 4.6 75k) did the same thing back in June but just while driving around town. This truck pulls the boat about 10 times during summer for a round trip of 20 miles. The code said trans overtemp and gets set when the temp exceeds ~260 degrees. I went for a drive with the scanner hooked up and the temp was up to 290 degrees. I did not really believe it at the time. The tranny should have stopped working with a bad smell of burnt oil and did not have or do that.

I changed the tranny fluid and blew out the cooler lines. The fluid was a brownish cooler but no burnt smell(1st time the tranny fluid has been changed). There was a flim of black material on the bottom of the pan from the clutch discs which I expect from normal operation. But no metal flakes or material.

Went for another ride and this time took the IR (infared red) gun. After 30 minutes I had 240 on the bottom of the tranny pan and 160 degrees coming out of the cooler going back to the tranny. That tells me the cooling system is working. Plus the fluid pressure on my scanner will only display 110psi. I hooked up a gage to the tranny and had the requried 220ish psi. I am really leaning towards something electronic not working properly.

I don't have your shifting symptoms thou. This one is shifting up and down just fine. I went to a local tranny shop and spoke with the owner who has been in business for 30 years. I shared my info and he's with me. Seems to be a sensor problem. I'm leaving it the way it is for now and monitor very closely. I plan on changing the trans fluid agian soon. I was not able to drain the torque converter and it holds alot of fluid.

Pull the dipstick and lay it across a clean light colored rag or shop towel. What color is it? Does it smell? At a minimum change the fluid and take it for another ride without the trailer and then with. Good luck.

 

The thermal sensor element in the trans is a very reliable piece,and I've never seen one bad unless it was broken from rough handling. On all '98-present 4R70/4R75 transmissions,it's located in the black "circuit board" electrical interconnect on the solenoids in the pan.
What exact code number are you guys getting? Pretty much every aftermarket code scanner I've seen has bad information on the code descriptions in the manuals.
JL

 

Are you using the correct mercon 5 fluid in the trans? Are you pulling that trailer with the O/D on or off? Does your truck have either the factory auxilary cooler or an aftermarket cooler installed? The one in the radiator is not enough when towing in the heat!

 

My code was P1783 Transmission Over Temp Condition. Thanks for the info on where it's located. I was hoping it pernetrated thru and I could just swap it out. I have not gotten a code since changing the fluid. Have you seen aftermarket scanners display bogus information to?? Data from other parts of the engine seem to be correct, voltage, engine temp, O2mv, speed etc.
Thanks

 

The code I pulled was P1783. I am pulling with the O/D off. I have an aftermarket cooler that is going to be installed next week-end. I had the transmission flushed about a year and a half ago, what they refilled it with I am not sure.

 

OK,that is the correct description.....I've seen aftermarket scanners show all kinds of goofy data depending on what you're trying to datalog. It's possible that the fluid got that hot for a very short time-esp if the TCC was unlocked for a period of time-fluid will get scorching hot in a very short time if the TCC is unlocked and the vehicle is in 3rd or OD at low speeds.
JL

 

Even though it's a bit messy I like to do my own transmission services. That way I know exactly what kind of fluid was put in. Some shops will use a bulk type of mercon fluid & then add a additive. The truck doesn't call for this, it does call for mercon 5 fully synthetic fluid. In your case they might have used the right stuff, I guess this is for others to know in the future.

I am not sure what the exact problem is with your trans, others on this site will be much more help then I could be. Whatever you do, fix it or replace it, get that cooler on there!!!

Sorry I couldn't be more help.