Note: Now removed stock cooler altogether and used one larger cooler. Click here for info.

Having identified that an engine overheating issue was directly related to transmission temperature, an additional transmission cooler was added.

The Problem
When off-road or at highway speeds the engine temperature would rise to 235F or higher and would continue to rise if ignored. The addition of a lift kit, larger tires and high outdoor air temperatures no doubt all contributed to this. Initially, it was identified as only an engine overheating issue, but subsequent investigation demonstrated that the high engine temperatures were directly related to relatively high transmission temperatures, 215-225F. Only when the transmission reached these temperatures did the engine have overheating issues.

The transmission fluid was burnt, cloudy and no longer clear within 2,000 miles of the start of the over heating issues. There is no doubt serious damage would have occurred to the transmission and engine if the problem was not addressed. As to whether or not the bad ATF was causing the problem or a result of the problem is unclear. At 30,000 miles it was noted that the ATF was turning very dark red and a fluid change would be required in the near future anyway.

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
It was decided to add an additional transmission cooler behind the front grille and in series with the existing coolers. For this, a Hayden Ultra Cool 404 (7 1/2" x 15 7/8") transmission cooler was used. The unit comes unpainted, so was painted flat black, apart from the connectors.

The passenger side of the dedicated cooler was disconnected and there is just enough room to move the stock pipe over to the passenger side of the cooler so that a new connection can be made to it. A female fitting can then be connected to the stock pipe connector and a male to the stock cooler. Pipe thread sealant was used on the threaded connectors.

To mount the new cooler, some pieces of door seal strip were placed on the supports between the new cooler and hood brackets behind the grille and just zip tied in place.

Some stainless steel braid cover was placed around two sections of 3/8" oil/transmission cooler hose and taped in place at only one end. One end of each piece was connected to the barb fittings at the stock tranny cooler and secured with stainless steel clamps. The easiest way to make sure the hoses will not snag when the hood is closed, is to make them extra long and not connect them at the new cooler end, but just zip tie them to the barbed connectors, then close the hood and check everything. Once you have them the right length, cut them to size, tape the stainless braid in place, connect them and clamp them in place.

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 around 25F cooler on the highway, and rarely goes above 190F when off-road. The transmission ATF and filter was changed at the same time as adding the new cooler. After 5,000 miles the transmission ATF looks perfectly clear and no leaks at all have been observed.

As no stock hoses or pipes have been cut, should you have a failure of the new cooler or hoses at any point, you can easily remove the connections at the stock cooler end and reconnect the stock cooler as it was before.

Update: This system was changed and the stock cooling circuit was totally replaced with one cooler and an extra capacity transmission pan installed.

Replacement Transmission Cooler
Aluminum Transmission pan

Click on an image below to enlarge

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