One of the most common, if not THE most common, problems associated with trailer towing is engine overheating. If you have a standard cooling system, without an expansion tank, you'll definitely need to get an aftermarket expansion tank kit, preferably one with at least a 2 quart (1.89 liter) capacity. These kits are easily installed on the radiator's overflow hose, and come with a pressure cap designed for expansion tanks.
Another helpful accessory for vehicles using a belt-driven radiator fan is a flex fan. These fans are large diameter units which are designed to provide more airflow at low speeds, with blades that have deeply cupped surfaces. The blades then flex, or flatten out, at high speeds, when less cooling air is needed. These fans are far lighter in weight than stock fans, requiring less horsepower to drive them. Also, they are far quieter than stock fans. If you do decide to replace your stock fan with a flex fan, note that if your car has a fan clutch, a spacer will be needed between the flex fan and water pump hub.
Aftermarket engine oil coolers are helpful for prolonging engine oil life and reducing overall engine temperatures. Both of these factors increase engine life. While not absolutely necessary in towing Class I and some Class II trailers, they are recommended for heavier Class II and all Class III towing. Engine oil cooler systems consists of an adapter, screwed on in place of the oil filter, a remote filter mounting and a multi-tube, finned heat exchanger, which is mounted in front of the radiator or air conditioning condenser.
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.
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.