What is the difference between internal and external transmission oil coolers?

Answer 1

An internal cooler is a small internal radiator inside the lower end of a regular radiator. It has two lines running to it from the transmission. This internal radiator gets cooling from the "coolant" that flows through the radiator regularly during running of the vehicle. The reason it is at the bottom of the rad (usually a veritcal flow type) is that the hot coolant comes into the rad at the top and then is cooled as it falls to the bottom. The smaller internal rad is also cooled by this "cooler" coolant (antifreeze and water mixture) and thusly cools the hot Transmission Fluid. This internal rad is separate from the regular cooling system and is a "closed System" within a system. An EXTERNAL transmission cooler is a small rad that is used exclusively for cooling of the automatic transmission fluid. It is completely separate from the rad but many times is mounted in front of the radiator. External coolers have much more volumetric efficiency and can handle larger quantities of fluid. They are installed on anything that may have a trailer towing package. Automatic transmissions get very hot while towing and need the extra cooling if they are pulling a load.