Transmission Stumble

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Rocket Man

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@donjetman is spot on about the flow order. However, it flows from the transmission into the bottom of the radiator fluid cooler, and out the top of it to the aux transmission cooler, then back to the transmission.
Yes, out of the bottom port of the trans to the bottom port on the radiator., then out the top port of the radiator and then either to an external cooler or to the top,port of the trans.
 
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Tim907356

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Bingo. The local transmission shop concurs as well. The thermostat is installed and ready for the 405mi. trek to Cincinnati tomorrow morning...
And, which one of you is picking me up along the highway when it blows? ;)
JK!
Thanks for the help! Good to have experts around.

Edit - it comes out of the TOP port of the TX to the bottom of the radiator, then from the top of the radiator to the aux cooler, then back to the TX at the bottom port.
(see the confusion?)
 
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Geotrash

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Bingo. The local transmission shop concurs as well. The thermostat is installed and ready for the 405mi. trek to Cincinnati tomorrow morning...
And, which one of you is picking me up along the highway when it blows? ;)
JK!
Thanks for the help! Good to have experts around.
You may run into trouble in the summer, if it's the kind of thermostat that stops the oil flow through the coolers. The 2015-2020 trucks had thermostats in their transmission cooler circuits that caused problems in hot weather. By the time the thermostat opens (I forget at what temp) under towing conditions, the thermal rise is happening faster than the cooler can overcome, causing temps to spike higher than they would without the thermostat inline. I believe there is a TSB to remove the thermostat on trucks so equipped to keep the fluid flowing through the coolers.

I went with a Derale 13960 fan-assisted cooler, mounted where yours is. It allows fluid to flow all the time, but the fan kicks in to help once the fluid reaches 180ºF. In winter driving, my transmission temp seems to run between 140-160ºF once fully warmed up, and stays below 200ºF when towing. In the summer, I'll see spikes up to 235ºF when towing over a steep mountain pass, which is totally fine for the 6L80E. It cools back down quickly afterwards, thanks to the fan.
 
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Tim907356

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You may run into trouble in the summer, if it's the kind of thermostat that stops the oil flow through the coolers. The 2015-2020 trucks had thermostats in their transmission cooler circuits that caused problems in hot weather. By the time the thermostat opens (I forget at what temp) under towing conditions, the thermal rise is happening faster than the cooler can overcome, causing temps to spike higher than they would without the thermostat inline. I believe there is a TSB to remove the thermostat on trucks so equipped to keep the fluid flowing through the coolers.

I went with a Derale 13960 fan-assisted cooler, mounted where yours is. It allows fluid to flow all the time, but the fan kicks in to help once the fluid reaches 180ºF. In winter driving, my transmission temp seems to run between 140-160ºF once fully warmed up, and stays below 200ºF when towing. In the summer, I'll see spikes up to 235ºF when towing over a steep mountain pass, which is totally fine for the 6L80E. It cools back down quickly afterwards, thanks to the fan.
This is a 2010; to my knowledge there's no internal thermostat. It certainly doesn't work if it's there, as it ran at 80-95deg. on the last trip.
 

Rocket Man

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Bingo. The local transmission shop concurs as well. The thermostat is installed and ready for the 405mi. trek to Cincinnati tomorrow morning...
And, which one of you is picking me up along the highway when it blows? ;)
JK!
Thanks for the help! Good to have experts around.

Edit - it comes out of the TOP port of the TX to the bottom of the radiator, then from the top of the radiator to the aux cooler, then back to the TX at the bottom port.
(see the confusion?)
I don’t know why you keep saying that, I’m 99% positive it flows out of the bottom port of the trans to the bottom port of the radiator. That’s stated everywhere I read, and I’m positive the lines don’t cross as they run forward on mine, bottom of trans to bottom of radiator.
 

Rocket Man

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You may run into trouble in the summer, if it's the kind of thermostat that stops the oil flow through the coolers. The 2015-2020 trucks had thermostats in their transmission cooler circuits that caused problems in hot weather. By the time the thermostat opens (I forget at what temp) under towing conditions, the thermal rise is happening faster than the cooler can overcome, causing temps to spike higher than they would without the thermostat inline. I believe there is a TSB to remove the thermostat on trucks so equipped to keep the fluid flowing through the coolers.

I went with a Derale 13960 fan-assisted cooler, mounted where yours is. It allows fluid to flow all the time, but the fan kicks in to help once the fluid reaches 180ºF. In winter driving, my transmission temp seems to run between 140-160ºF once fully warmed up, and stays below 200ºF when towing. In the summer, I'll see spikes up to 235ºF when towing over a steep mountain pass, which is totally fine for the 6L80E. It cools back down quickly afterwards, thanks to the fan.
The aftermarket thermostats that TruCool (and I believe Derale too) sell are the type that start to open at 180 and are fully open at 205. That’s the reason I didn’t install one. They say they’re for real cold climates but imo 180 is too high a temp to stop fluid from flowing. Maybe if that was 120, I’d be ok with it. I can understand wanting to heat the fluid up some, but to keep it at a minimum of 180 is too hot for me.
 

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