[Steve C.]

Fluid Coolers
Most hot rodders know that a tranny cooler is something they should install, but many just haven't made the time to do so. Unfortunately, such a casual attitude may not be the right approach. "In any place other than Antarctica, you should install a transmission fluid cooler," opines Stan. "Anytime you separate the cooling of the transmission fluid from the radiator, where the temperature can run over 210 degrees, you will promote longer transmission life. Instead of the transmission fluid only being cooled to the temperature of the radiator coolant, it will now run about 20-30 degrees cooler than the engine by using a separate transmission cooler."

TCI Automotive

Comment from another source:

Line routing
"Auxiliary transmission coolers are more effective when routed in the return line of the transmission cooler rather than the feed line."

Another source:

"The most often asked question is should I bypass the radiator cooler when I install a auxillary cooler.
Most cooler manufactures and automobile manufactures information we have read, recommends installing the coolers In-Series with the factory radiator cooler for maxium cooling efficiency. So unless the manufactures who have spent 1000's of hours testing different installations are wrong, the suggested cooler installation is in-series. If you must bypass the radiator because the cooler tube is leaking or for other reasons, be sure to increase the size cooler you install by 1 to 2 sizes."

Another source:

"There is two lines of thinking on how the cooler should be installed. One is so the fluid goes from the transmission to the auxiliary cooler, then through the stock cooler built into the radiator and then back to the transmission. The second method is to have it flow through the stock cooler, then the aux cooler and back. That is the way mine is currently installed at the suggestion of the pros at Level 10."


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[Singleton]

I would go thru the radiator first, then the auxiliary. Fluid cools, (or warms), to engine temp, then drops another ~20 degrees or so in the aux, before returning to trans. This should put the trans fluid temp around 160-175 depending on thermostat used.

From B&M:

B&M Super Cooler Mounting Guidelines
When considering installing a supplemental transmission fluid cooler B&M recommends the following guidelines for a successful and efficient installation:
● Route the transmission fluid through the stock radiator cooler, then through the supplemental B&M SuperCooler and then back to the transmission. This will provide the most efficient transmission fluid cooling system for your vehicle.