Hayden 678 Rapid-Cool Add-On Transmission Cooler

The Hayden 678 is an add-on plate-and-fin automatic transmission oil cooler that mounts ahead of the radiator or A/C condenser and plumbs inline on the cooler return line. It runs alongside the factory radiator cooler rather than replacing it, so ATF makes a second pass through outside air before it goes back into the transmission. The core measures 3/4 inch thick by 11 inches wide by 9-1/2 inches tall and is rated for vehicles up to 24,000 pounds GVWR and towing up to about 5,000 pounds — pickups, full-size vans, Class C motorhomes and travel trailers to 24 feet.

Heat is what kills an automatic. ATF that runs past roughly 240 degrees F loses its film strength and oxidizes, and every 20-degree jump above that roughly halves fluid life and cooks the clutch material and seals. Towing, stop-and-go, big tires and a locked-up converter all push pan temps up fast. Dropping fluid temperature back into the low 200s is the single cheapest thing you can do to make a transmission live, which is why a lot of rebuilders will not warranty a unit in a tow rig without an auxiliary cooler on it.

The plate-and-fin design flows more area than a basic tube-and-fin core, and Hayden's patented internal turbulation trips the fluid inside each plate so more of it touches the cooling surface, pulling heat out with very little added pressure drop. Fittings are hose barb and the cooler ships with the nylon-tie mounting kit and hose so you can splice it into the 5/16 or 3/8 inch steel cooler line at the radiator. Aluminum construction, about 1.1 pounds, one-year warranty. Ships from the USA; handling in 1-2 business days.