Engine/Transmission (1998.5 - 2002) 98.5 autotranny overheats.

[LeeB]

New thermostat and water pump. When it overheated in the past, both the engine and radiator overheated. This time it was only the trans.

 

[Vaughn MacKenzie]

If you are only doing 25 mph up a hill manually downshift to 1st gear and let it run higher RPM. Auto trannies are set to upshift so fast you're likely in 2nd or 3rd gear out of lockup and torquing right through you converter.

 

[LeeB]

Ok, been studying some and now see that lockup occurs as engine and transmission rpm become about the same. Couple of questions. Can and does lockup occur in lower gears? What effect does manually locking up with a lock up switch at lower gears have on the TC and transmission? At what point is it safe to do a manual lock up? And last but not least, could my overheating problems be partially due to a bad TC? The transmission on this truck was replaced with a rebuilt one just before I bought it. Don't know about the TC. I may be able to find the reciepts and see once I get back home. I really don't feel the load being pulled was excessive and the hill was only a couple hundred yards at most. I'll ask the wife about what gear and range she was in tonight when I talk to her.

 

[cerberusiam]

Locking the TC takes the sloppy stock fluid coupling out of the equation. The fluid coupling is what generates the bulk of the heat in the trans.

If the TC works correctly in normal driving there is nothing wrong with it, that is just the way they were built. One of the big reasons most of us replace them with a custom stall, fluid coupling and billet cover. If you work the truck hard the stock TC is a huge liability.

IIRC you will not be able you lock the TC in 1 or 2 without modifying the VB. Prettu sure that feature was disabled in the early 47RE's. Locking the TC in the lower gears allows use of those gears in high load situations to get the power on the ground and limit the heat build up.

Not sure you have a heating problem at this point. Given the age of the truck the factory sensors are not the most accurate. You need a gasuage in the front cooler line on the tran so you can monitor actual temp and adjust driving to keep it in check.

 

[LeeB]

It was hot. No doubt about that. And as I said, not the first time. I had hoped changing the thermosta and water pump would have helped and it did with the engine temps. New fan clutch, radiator, aircooler, and intercooler. Had to replace all that after an unplanned custom body job. She was in 4high and drive w/ the OD off.

 

[cerberusiam]

Hot is one thing, overly hot is another. Until you can monitor a temp that makes sense it is still a guessing game. In 4HI and D on a soft road with a dead weight pulling at low speeds the TC wasn't locked and it was generating massive amounts of heat in the fluid coupling, that is normal. Dropping it into 2nd or even 1st would have increased the air flow and the leverage to where it likely would not have gotten that hot.

Everything you are detailing at this point does not indicate a mechanical issue, rather, it is indicative of an operational oversight. You can't know that for sure until you add a gauge that will monitor the temps in the correct spot, adjust the driving style, and monitor the results. You can start throwing parts at it hoping to find the solution, or, add some monitors and test the results.

 

[LeeB]

It was overly hot. Exactly how hot I can't say because as you have said, I have no gauge and can't put one on until I get back home. I have no desire to throw parts at it, exactly the opposite. That's why I came here to try and learn something. Driver error quite likely compounded the issue. We have always driven standards and have never had issues like this. Hence my ignorance of Auto transmission issues. Please bear with me on this. I do appreciate the help.

 

[LeeB]

Put it in the shop. The TC and two solenoids were bad.