FAQ - Transmission Oil Coolers

The transmission cooler in the radiator is leaking and is expensive to repair. Can I use a Hayden transmission cooler to eliminate it?

Answer:  Yes. Always choose one of the larger Hayden coolers when eliminating the radiator cooler to compensate for the loss of cooling from the radiator. In most installations we recommend use of the radiator tank cooler to provide maximum cooling and to comply with most manufacturers warranties.

Should the cooler be installed before or after the radiator?

Answer:  We recommend installing the auxiliary cooler after the radiator to return the coolest fluid directly to the transmission. Installing the cooler before the radiator will still provide additional cooling and may be necessary in some difficult-to-access applications.

Can you over cool the transmission fluid?


Some transmission problems really are unique to the cold weather while others get worse. Metal components contract as they get colder which results in component mates loosening up, parts wearing quicker due to friction from reduction in clearances between components, and can develop leaks from shrinkage and hardening of seals and gaskets.

The ideal operating temperature for a transmission is 180°F. The viscosity of transmission fluid changes and gets more viscous at lower temperatures. As the transmission fluid (ATF) falls below 32°F, its viscosity becomes significantly higher, restricting where it can flow to lubricate the internal components of a transmission, leading to premature wear. The use of synthetic ATF fluids is recommended where its viscosity at cold temperatures is lower than petroleum based ATF fluids.

It is critical in extreme cold conditions to use the original equipment cooler in series with an auxiliary or by-pass cooler and allow the vehicle to warm up before driving.

What is the difference between an Ultra-Cool and Rapid-Cool transmission coolers?

Answer:  Ultra-Cool is a tube and fin (serpentine) design that is a time proven cost effective design. The round tube design is the strongest and most reliable cooler design. The Rapid-Cool design is a plate and fin design similar to most radiator designs. The flat plates allow more contact with the cooling air. This provides a design that is about 33% more efficient size-for-size than comparable Ultra-Cool models.