An automatic transmission is usually recommended for trailer towing. Modern automatics have proven reliable and, of course, easy to operate, in trailer towing. The increased load of a trailer, however, causes an increase in the temperature of the automatic transmission fluid. Heat is the worst enemy of an automatic transmission. As the temperature of the fluid increases, the life of the fluid decreases.
It is essential, therefore, that you install an automatic transmission oil cooler. The oil cooler, which consists of a multi-tube, finned heat exchanger, is usually installed in front of the radiator or air conditioning condenser, and is connected inline with the transmission's radiator cooling tank inlet line. Follow the cooler manufacturer's installation instructions.
Select an oil cooler of sufficient capacity, based upon the combined gross weights of the towing vehicle and trailer.
Cooler manufacturers recommend that you use an aftermarket cooler in addition to, and not instead of, the present cooling tank in your radiator. If you do want to use it in place of the radiator cooling tank, get a cooler at least two sizes larger than normally necessary.
NOTE: A transmission oil cooler can, sometimes, cause slow or harsh shifting in the transmission during cold weather, until the fluid has a chance to warm up to normal operating temperature. Some coolers can be purchased with, or retrofitted with, a temperature bypass valve which will allow fluid flow through the cooler only when the fluid has reached a designated operating temperature.