The Problem
After having already added an additional transmission cooler, transmission and engine temperatures were running within accepatble limits. However, the many reported cases of main radiator failure, allowing transmission fluid and coolant to mix together, were of some concern, especially on a vehicle no longer covered by warranty. Transmission temperature would also still get a little hot when the torque convertor was out of stall (not locked up) for extended periods.

Stock Transmission Cooling
The transmission is cooled in two places, the passenger side of the main radiator core and the transmission cooler in front of the main radiator core. Both of these will have some effect on the temperature of the engine coolant section of the radiator core.

The Solution
The stock transmission cooler, as well as the additional cooler added previously, were both removed. The main radiator element of the cooling circuit was disconnected and the radiator plugged to prevent coolant loss in the event of failure of the partition between coolant and transmission fluid. A Hayden 405 Ultra Cool (10" 15.5" x 3/4") transmission cooler was mounted in the stock location.

It should be noted that the main radiator core does act as an heat exchanger to some extent. In cold climates it will warm up the transmission fluid, as optimum operating temperature is around 175F. In warmer climates, this is unlikely to be a concern.

First everything was removed, the stock cooler, the additional cooler previously added, all unnecessary pipes/hoses/etc. Everything forward of the stock cooling circuit from the two connectors at the base of the main radiator was removed. It was easier to remove the passenger side wheel well liner to access the lower connectors at the main radiator. Two blanking plugs were used to plug the radiator.

The rivets holding the stock cooler to the mounting bracket were drilled out. The Hayden 405 was put in place in front of the a/c radiator with the mounting bracket over the top and the location of the mounting holes marked. Both were then removed, and the through radiator mounts supplied with the cooler were used to attach the transmission cooler to the stock mount.

Braided hoses were attached to the cooler and the complete assembly was mounted in the stock location. It is easiest to leave the hoses a little longer than required, then cut them to the exact length you want after they have been routed, making suring to leave a couple of inches to slip over the existing pipes.

Double check all fittings and top up transmission fluid as required. Thoroughly clean the area of any spilled ATF, so identifying leaks is easier, and after a test run check for any leaks, check again in 500 miles.

The transmission now runs at around 185F on the highway, and reaches 200-205F with the torque convertor out of stall (generating most heat) running against a strong head wind at 70 mph. Engine temperature stayed consistent at 200F.

Update: On long trips the transmission still gets hot (225-230F) when out of stall for a long time. When stalled it runs cool.

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