Written by Mike Steen - Technical Director
External cooler by-pass valves are becoming more and more popular it seems. There are also many different variations of these by-pass valves. It’s important that you check the cooler lines and cooler closely to see if the vehicle your working on has one of these by-pass valves. In most cases they can be removed and cleaned.
Most all automatic transmissions incorporate some sort of by-pass in case the cooler becomes restricted, but they are typically found inside the unit.