Hot Transmission

So a couple of weeks ago I was pulling my trailer up the mountain and it was over 100 degrees outside. Everything was fine until I got to a particularly long, steep part and my transmission started getting too hot and the OD light began flashing. I had to pull over to let it cool. I ended up having to let it cool three times to make it to our camping spot. On the way back down the mountain we travelled early in the morning. The transmission was getting hotter than usual, but not too hot. But what was strange was that both times, going to and from, the transmission would not get any cooler on steep downhills with zero load on it. After we stopped for lunch the transmission began acting completely normal for the rest of the way home, but the OD light was still blinking.

At home I tested for the code and all I got was the code telling me to turn my AC off and try again. So I did that, but my code reader had already erased the code. So I guess I have to pull my trailer up a mountain during a heat wave to throw the code again, because now it's working fine.

I have a large transmission cooler installed. The fluid runs through the cooler first and then through the radiator. I think I'm going to try switching the order. Although the motor temp was probably 220 to 225 at the hottest. I was shutting it down when the transmission reached about 250.

Any thoughts?

You were working the transmission pretty hard, in high temperatures. I'd expect it to heat a bit above normal, but don't know how much.

My transmission fluid runs: transmission--->radiator---->aux cooler---->transmission. Let the radiator do an initial cooling, so the aux cooler has a lower start point. You say a "large cooler". Which one?

At this point, after running hot that way, I'd check whether you burned the transmission fluid.

Its a True Cool transmission cooler. It was the biggest one that they made at the time. I think this one is it (8.5"x22.75"x1.25"):
https://www.amazon.com/Tru-Cool-LPD47391-Pressure-Transmission-Cooler/dp/B0060NKA1U/ref=sr_1_35?crid=3FSYFSHMTBSSV&dchild=1&keywords=transmission+cooler&qid=1599511579&sprefix=transmission+,aps,238&sr=8-35

It is mounted right behind the grill, in front of both the radiator and AC coil.

Yeah, I'm draining the fluid right now. It just smells slightly burnt, if any, and is a little darker than new.

I have the same cooler, mounted in the same spot. That cooler is certainly up to the job. I'd suggest changing your flow order. Have the fluid go through the radiator and then the cooler, then back to the transmission.

Always add any aux coolers after the radiator. The radiator is your primary cooler.

Excessive heat and burnt/slightly burnt fluid is a sign of slippage. Change the fluid and drive it.

Any guess as to what code it was throwing? Is there an overheat code?

WarNose said:

Any guess as to what code it was throwing? Is there an overheat code?

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There is no code for overheating.

Code 62 is the most common. Converter clutch failure. The TCM detects this by reading the signal from the TPS, tach, and VSS. If the signals are out of range this code will set.

trackspeeder said:

There is no code for overheating.

Code 62 is the most common. Converter clutch failure. The TCM detects this by reading the signal from the TPS, tach, and VSS. If the signals are out of range this code will set.

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Assuming that was the code, would that have been a temporary condition because of the high heat? is it something that I need to worry about or will it rectify itself if I change the fluid and fix the cooling system?

If the converter lockup clutch failed, it would also cause excessive heat

Philip1 said:

If the converter lockup clutch failed, it would also cause excessive heat

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It seems like that might have been what happened. I was turning the OD button on and off kind of frequently to help me get through the curves and grade on the mountain. I feel like that had something to do with it.

Yeah on those types of hills when loaded I try to leave the OD off and leave it in a particular gear (3rd/2nd etc) for the duration, instead of shifting back and forth for short periods of time in each gear.

WarNose said:

Assuming that was the code, would that have been a temporary condition because of the high heat? is it something that I need to worry about or will it rectify itself if I change the fluid and fix the cooling system?

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Change the fluid and drive it. Most likely it was the conditions that caused it. I doesn't take much for the TCM to throw a 62 code. One little slip and this will show up.

WarNose said:

It seems like that might have been what happened. I was turning the OD button on and off kind of frequently to help me get through the curves and grade on the mountain. I feel like that had something to do with it.

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In a case like this, leave the OD off. If the curves and grades are really tough, manual 2nd.

I recommend full synthetic transmission fluid. It is much less likely to "burn" or deteriorate under high temperature conditions. Most well known brand names manufacture full synthetic fluid, Valvoline, Mobil 1, Red Line....

Do you guys recommend that I flush the transmission or would just draining what's in the pan good enough?