Hayden 1240 Heavy-Duty Transmission Oil Cooler, 6 x 18 in

The Hayden 1240 is a heavy-duty tube-and-fin auxiliary oil cooler measuring 6 by 18 by 1-1/2 inches in a single-pass design. The core is brazed copper tube with aluminum fins and a copper header, and every tube carries an inner-swirl turbulator that spins the fluid against the tube wall for roughly three and a half times the cooling surface of a plain tube. Inlet and outlet are 1/2-inch female pipe thread, and the cooler comes with rubber-block vibration mounts and hardware to hang it in front of the radiator or condenser.

Hayden rates the 1240 for transmission, engine, gear box, and hydraulic oil, which is why it turns up as much on Class 8 trucks as on tow rigs. It is a common direct replacement for the water-to-oil transmission cooler on Eaton Fuller 9-, 10-, and 13-speed gearboxes in Kenworth, Peterbilt, and Volvo trucks, getting the transmission off engine coolant and onto its own air-cooled loop.

Heat is what kills an automatic. Fluid that runs past about 250 degrees oxidizes, cooks the clutches, and takes converter and pump life with it. Plumbing a 1240 in series after the factory cooler, on the return line back to the transmission, pulls another chunk of temperature out before the fluid re-enters the case, which is cheap insurance under towing, plowing, or stop-and-go loads. Mount it where it gets clean airflow, match the fittings and line size to your transmission's flow, and use the supplied rubber blocks so vibration does not fatigue the tubes.