Transmission Heat Exchangers & Coolers

By Chris, Hale Marine · 40+ years rebuilding Velvet Drive and ZF transmissions

Short answer: Replace transmission coolers about every five years in fresh water and every two years in salt water, and right away if metal or water has gotten into the transmission.

Chris calls it the number one rule: replace your transmission coolers. In fresh water, including the Great Lakes, that's about every five years. In salt water, particularly in Florida where you're going over a lot of sand and through inlets, it should be every two years.

If metal has been through your transmission, you must replace the cooler. All that metal is going to get in the cooler, get stuck between the tubes, and it cannot be flushed out. The same goes for water: if you get water in a transmission, replace the coolers immediately.

Cooling problems can also come from what gets into the cooling circuit. We had a transmission come in from Georgia that got hot, and there were leaves and stuff inside the cooling circuit.

Browse coolers below by the engine brand you're pairing them with, or see when to replace your transmission cooler and why transmissions overheat for more detail.