Hi all. I have a 2005 Yukon XL Denali and wondered if anyone else has had success doing a radiator bypass for the tranny lines, and just using an Aux cooler on the front? Issue 1: From the factory, GM and other manufacturers run the transmission lines through the main radiator and it shares space with the antifreeze (separated internally). If anything internal cracks inside the radiator...bye bye transmission. This has happened to quite a few people and seems absurd to design it this way. Issue 2: The radiator/thermostat want to operate at 180 degrees. Why in the hell would we want to heat the tranny fluid to 180 then try to cool it again in a tiny little cooler on the way back to the tranny? It seems to me that the best solution would be to just bypass the big radiator, thus reducing the risk of blowing my transmission if the radiator leaks/cracks/mixes antifreeze in my tranny fluid. Then I would need to install a larger aux cooler on the front to make sure temps stay low. Is there a downside I'm missing to this? I know that some people think the reason it's designed this way is to actually heat the tranny fluid up on cold days, but given that it wrecks my towing and temps in the mountains, I think I'd rather just disconnect.

The thermal management 'SYSTEM' has more to do than you seem to think about...Also, your profile says Colorado, so extreme cold...subzero even for long stretches of timeBy changing the thermal management system by not having the ATF go into the main coolant radiator...you might have ATF that is too cold during those subzero timesThe sizing of both the ATF external aux and the ATF internal radiator in the cold tank of the main radiator accounts for both the cooling and heating of ATF AT SPECIFICATIONS during all aspects of your vehicle...including using it as a TV towing heavy (up to the specification limits)Ever notice semi's running in subzero ambients will cover a portion to totally cover their radiator intake/grill ?Recommend keeping the routing into the main radiator and installing another or bigger ATF Aux external radiator

I don't think it's more than I've thought about. if I did the bypass I'd probably hook it back up if I ever sold it to someone else. For my situation...I only use the Yukon for trips/towing, the rest of the time I drive a car or my van, so my purpose is very specific. I also have it garaged with insulation, always 45 degrees + here. My biggest beef with running the tranny fluid through the radiator is the damage it can cause if it cracks internally. Do a little googlin' and you'll find countless threads with this. It's like built in obsolescence IMO.

I didn't Google it, but in my long experience, I think your worrying about something that is pretty rare. I've never heard of it happening. If you maintain your radiator and coolant, you shouldn't have a problem. The only way for it to crack is if something rusts or corrodes. Not enough pressure in the transmission lines to crack on their own. It's not like it pools in the radiator. It is a sealed system.

I think you are assuming too much. http://www.topix.com/forum/autos/gmc/T7G5S6Q7Q5B2BSC0D/denali-transmission-cooler-failure-ruins-transmissExamples of a car with 74k miles having the issue. Nissan did this on the Xterras for a few years too, then they fixed the problem by not routing it through the radiator. Nissans was a much wider spread issue, but it was a lot easier to bypass too with flex lines instead of stainless.

The in-tank cooler is not getting 180F coolant flow. It's on the "cool" side of the coolant path, so it should be close to ambient, unless you're working really hard, in which case it will still be much cooler than the ATF temps.Water-to-oil is still more efficient at heat transfer than air-to-oil, that's why the OEMs still use in-tank coolers.

Bypass radiator/tranny cooler combo? | Good Sam Community

33 Replies

RSD559
Explorer
Jun 30, 2017
I didn't Google it, but in my long experience, I think your worrying about something that is pretty rare. I've never heard of it happening. If you maintain your radiator and coolant, you shouldn't have a problem. The only way for it to crack is if something rusts or corrodes. Not enough pressure in the transmission lines to crack on their own. It's not like it pools in the radiator. It is a sealed system.
jlrosine
Explorer
Jun 30, 2017
I don't think it's more than I've thought about. if I did the bypass I'd probably hook it back up if I ever sold it to someone else.

For my situation...I only use the Yukon for trips/towing, the rest of the time I drive a car or my van, so my purpose is very specific. I also have it garaged with insulation, always 45 degrees + here.

My biggest beef with running the tranny fluid through the radiator is the damage it can cause if it cracks internally. Do a little googlin' and you'll find countless threads with this. It's like built in obsolescence IMO.
BenK
Explorer
Jun 30, 2017
The thermal management 'SYSTEM' has more to do than you seem to think about...

Also, your profile says Colorado, so extreme cold...subzero even for long stretches of time

By changing the thermal management system by not having the ATF go into the main coolant radiator...you might have ATF that is too cold during those subzero times

The sizing of both the ATF external aux and the ATF internal radiator in the cold tank of the main radiator accounts for both the cooling and heating of ATF AT SPECIFICATIONS during all aspects of your vehicle...including using it as a TV towing heavy (up to the specification limits)

Ever notice semi's running in subzero ambients will cover a portion to totally cover their radiator intake/grill ?

Recommend keeping the routing into the main radiator and installing another or bigger ATF Aux external radiator

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Bypass radiator/tranny cooler combo?

33 Replies

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