Why are Transmission Coolers Installed on the Fluid Return Line After the Radiator Mounted Cooler

Expert Reply:

The biggest reason that transmission cooler manufacturers and vehicle manufacturers want transmission coolers installed after the factory cooler rather than before it is because the transmission cooler in the radiator is surrounded by the coolant in the radiator. The transmission fluid leaving the radiator mounted cooler can be cooled further by the aftermarket transmission cooler.

Installation before the OEM radiator mounted transmission fluid cooler would negate most or all of the aftermarket coolers effectiveness. If you installed the aftermarket cooler before the radiator, the fluid would be cooled by the aftermarket cooler and then would be warmed by the radiator mounted cooler and would likely not be much, or any, cooler than it would be without the cooler installed when the engine is up to normal operating temperature.

There is also a slim possibility that transmission line pressure could be great enough to push one of the hoses off of the transmission fluid supply line. Installing the cooler after the OEM cooler on the return line reduces this possibility.

expert reply by: Bob G