How is it that my Transmission and Engine Overheted at the same time?

The automatic transmission on my 1997 Chevy Silvarado 6.5 diesel turbo charge was having an issue switching from 3rd to 4th gear. Actually it never made it to 4th until the next morning when it had a chance to cool down. I was hauling nothing at that time.

I brought it to a local mechanic who changed the TCC solenoid and 2 shift solenoids.

I picked it up from the shop and drove it literally 10 miles and the next thing I knew I was sitting on the side of the road waiting for a tow truck. Apparently, the transmission overheated to such a degree that the new transmission fluid, just installed, had just burnt up and I was unable to move the truck. The trucks temperate had gone as high as 230 degrees.

How could have this had happened especially considering the addition of the new fluid as well as the new solenoids? Any advice would be appreciated as I was stuck with an $1,800 repair bill. I feel as though the local mechanic did something wrong and want to determine how this could have happened.

I can’t tell you what caused the transmission fluid to become burnt in only 10 miles after the repair, but it can happen.

If the transmission begins to slip it creates a lot of heat. This burns up the tranny fluid. As this heat builds up in the tranny, the tranny fluid that passes through the radiator tranny cooler starts heating up the coolant in the radiator. If the coolant temperature increases it removes less heat from the engine. Then the engine starts to run hot.

This works both ways. An overheating automatic transmission can cause the engine to overheat. And an overheating engine can cause an automatic transmission to overheat.


As I recall automatics use a radiator in the same area as the engine’s radiator, so when one gets hot, the other also tends to get hot.

What you need to do to help keep this from happening again is to install an external transmission cooler. This cooler works in conjunction with the transmissions radiator cooler which sits inside the radiator tanks. This is why both engine and transmission overheated at the same time. Transmission fluid needs to stay under 200 degrees. Transmission fluid starts to break down from 195-200 degrees and will break down faster the higher the temperature is. If you tend to tow a lot, I would buy the trans cooler with the electric fans installed. These run around $200. Mount the transmission cooler so that the line coming from the output of the trans goes to the input of the radiator cooler, then from the output of the radiator cooler to the input of the external cooler, then from the output of the external cooler to the input of the transmission.


Were there any indications that overheating was beginning to be a problem before the transmission began to break loose? The simultaneous overheating of the engine and transmission in such a short drive is peculiar. Was there any indication of a lack of power in that 10 mile drive? What was the ambient temperature? A restricted radiator or bad water pump or bad thermostat could cause the situation as you described but it seems unlikely that you would not recognize the problem before the transmission broke loose.

I was taking the mountain pass back to Palm Springs the day my transmission wouldn’t shift into 4th gear. During that drive I was constantly viewing the engine temperature gauge. The temp would get as high as 190 degrees but when I slowed down to around 45 miles/hour, it would drop to about 175. So, the engine’s cooling system seemed to be working fine. After the tranny was rebuilt, the temperature was normal and nothing was done to the cooling system.

My conclusion is that the transmission was creating a drag on the engine and that the tranny caused the engine to overheat. I am still trying to determine if the local shop did something that would have caused the tranny to overheat such as putting in a bad solenoid or switching the wires or something like that. If I can’t find a reasonable solution, then I will be eating $1,800. Ouch!!

On many vehicles…the tranny cooler and radiator share the same housing. Basically it’s just a radiator with a small section at the bottom (about 3-5 inches) for the tranny fluid. Years ago they use to sell different radiators for cars with standard or one with an automatic. Now it’s the same radiator…so if you have a standard…you just don’t use the bottom part of the radiator.

As Tester has explained the transmission overheat caused the engine to overheat. I am assuming that this truck has the 4L80-E transmission. The 3-4 clutch pack or the 4 band was slipping creating extra heating of the transmission oil. Changing the fluid, the TCC solenoid, and the shift solenoids was a vain attempt to save the transmission. Your transmission probably could not have been saved by any service procedure other than an overhaul.

What did the $1800 expense cover? Was it for the first service? If this is the cost for a rebuilt transmission plus R&R, that would be a great price IMHO but Transman618 could give you a better opinion on the amount you paid. Hopefully he will reply back.

The $1,800 covered the cost to rebuild the transmission and yes, it is a 4L80E.

So, in conclusion, it seems completely possible that with new transmission fluid, it only took 10 miles of driving time for it to burn up. Also, based on what I read thus far, it seems as though the 1st repair facility was not at fault considering that replacing the TCC solenoid and 2 shift solenoids would not have caused the damage that occurred unless I am missing something. I do know that they were having problems getting it to shift smoothly and that took another day in the shop.