Many people consider an auxiliary automatic transmission cooler for their vehicle. In some cases transmission coolers do offer benefits. Many of the claims for transmission coolers are overstated and, improperly installed, they may do more harm than good.

Automatic transmissions produce heat, and this is normal

Much like an engine, an automatic transmission has a preferred temperature. Under normal conditions, automatic transmissions operate at around 175 degrees Fahrenheit. Below this temperature, there may be moisture buildup and lack of efficiency. As temperature rises, there will also be problems.

All automatic transmissions have the means for cooling. Automatic transmission fluid brings heat from the internal components and transfers it to the transmission case and pan. Air passing by the case and pan, remove a great deal of excessive heat from the transmission. There is normally a cooler outside of the transmission as well. Most vehicles have a transmission cooler built into their radiator. In many cases this is more than adequate to maintain transmission temperature.

Overheating may be a symptom of a transmission problem

Automatic transmissions may overheat for a number of reasons. When a transmission starts to overheat, it is very important to find and correct the problem. It may be tempting to simply add an auxiliary cooler, but if the problem is internal, this will not help and may hurt.

Clues to diagnosis come from the history of the vehicle. If a transmission has not overheated in the past, and nothing has changed, the problem is likely internal to the transmission. Low pressure, from a restricted filter, may show as elevated transmission temperature. Internal failures, such as slipping clutches and a bad torque converter, will also cause temperature to rise. In these cases, transmission repair is the answer and adding a cooler will not help.

When is an auxiliary transmission cooler appropriate

Vehicles used for towing may sometimes benefit from an additional transmission cooler. Towing increases the load on the transmission, and this produces more heat. For example, a transmission that runs within the normal range of 175 to 200 degrees Fahrenheit when not towing and rises slightly above when towing, may benefit from an auxiliary cooler.

An auxiliary transmission cooler is NOT a silver-bullet

A transmission cooler will not help a truck that is overloaded. Elevated temperature in a transmission is a symptom, as well as a problem. Temperature rising into the 275 to 300 degrees Fahrenheit range indicates a vehicle towing more than it is capable of pulling. A transmission cooler cannot make up for a deficient design, and a heavier vehicle will be needed.

Properly installing an automatic transmission cooler

For an auxiliary cooler to operate, it must be properly installed. The best choice is to see if the manufacturer of the vehicle offers a transmission cooler for the vehicle. Purchasing the factory-option cooler and having it installed, prevents a great many problems. The factory cooler is designed to fit the vehicle. When aftermarket coolers are installed, several things need to be observed.

Hose problems

It is also best to place the auxiliary cooler inline with, and after the existing radiator cooler. With the factory installation kit, this should be easy, as all necessary fittings and lines are usually supplied. With an aftermarket cooler, lines must often be cut and hoses attached.

Cutting a metal line and clamping a hose to it, is very dangerous. Transmission fluid is the life-blood of the transmission and under high pressure. If the line pops off, the transmission will quickly burn up. Transmission fluid is also flammable and presents a hazard if a line comes off. Double clamps on a line without a barb, are useless and should not be attempted.

When a metal line must be cut, a compression ferrule may be used to create a barb and prevent the line from coming off. Slip the compression nut over the line, add the ferrule. Use a male compression fitting to lock the ferrule to the line. The compression nut may then be removed with a cutoff tool and a hose clamped on, using the ferrule to assure retention.

Transmission hose is a specialized product, designed to resist petroleum, heat and pressure. Only a hose that specifies, "for transmission use," should be used. The hose needs to be properly routed and secured to avoid chaffing and cutting.

Be careful when attaching hoses to the body of the vehicle. Before drilling holes, check both sides of the panel. Drilling into a brake or fuel line can create a real problem. Check bolts and screws to make sure they do not interfere with other components. This bolt rubbed through the air conditioner condenser and caused an expensive repair.

Mind the gap

Factory transmission coolers are designed with brackets that support them and provide an air gap between the cooler and other components. This gap is necessary for proper airflow.

The auxiliary cooler needs to be mounted in front of the air conditioner condenser or any other coolers. There also needs to be an air gap of between the cooler and the next component. The air gap should be between one-half and one-inch spacing. This allows for air flow and prevents the cooler from rubbing holes in other components.

This aftermarket transmission cooler is improperly installed. Attaching the cooler flat, against another component, will result in lack of cooling and other problems. Such an installation may be worse than not adding a cooler. If the radiator cooler is also bypassed, damage to the transmission may occur.

All vehicles vibrate and when components touch, problems will be close behind. The above cooler was attached to an existing brace with a tie strap. The brace will rub through the aluminum cooler and cause a dangerous leak.

Proper installation of an aftermarket cooler

This cooler is firmly attached with metal straps, at the proper distance from the condenser. The hoses are clamped over barbs and routed safely. After installation, and when towing, transmission temperature dropped from 225 degrees to 175 degrees Fahrenheit.

If a vehicle is experiencing elevated transmission temperature while towing, an auxiliary transmission cooler may help. With proper installation, an auxiliary cooler may help keep the transmission working for years to come.