Hayden 677 Rapid-Cool Transmission Oil Cooler 14,000 GVW

The Hayden 677 is a plate-and-fin auxiliary transmission cooler for rigs that run hot in traffic, on grades, or behind a small trailer. The core measures 11 in wide by 7.5 in tall and only 0.75 in thick, with a 5-1/2 in core height, so it fits in front of the condenser on most full-size cars, trucks, and SUVs without blocking the radiator. Inlet and outlet are 3/8 in push-on barbs, which is the size of the factory rubber cooler hose on the majority of GM, Ford, and Chrysler applications. Manufacturer part number OC-677.

Plate-and-fin is the design to use when you have the space for it. Fluid is routed through internal turbulators that break up laminar flow against the plate wall, so more of the fluid actually touches cooled metal instead of sliding past in the middle of the passage. That moves more heat than a tube-and-fin core of the same frontal area while keeping the pressure drop low enough that you are not starving the converter or the cooler circuit on a cold morning.

Heat is what kills automatics. Fluid life roughly halves for every 20 degrees F above about 175 F, and sustained pan temps over 240 F cook the additive package, glaze the frictions, and harden the seals until you are chasing slip codes and a flared 1-2. On a stock-cooler truck that tows, or a unit you just rebuilt and want to keep alive, an add-on cooler plumbed in series after the radiator cooler is the cheapest insurance on the vehicle. Rated for vehicles up to 14,000 GVW and towing up to 2,500 lb.

Ships with the cooler, hose, clamps, and nylon-tie mounting hardware, so the only thing you may need to buy separately is extra hose if the cooler is mounting far from the factory lines. Measure your available depth in front of the condenser and confirm your line size before ordering; this is a universal-style cooler, not a bolt-in replacement for a factory unit.