What is a Trans Oil Cooler Assembly?
Transmission oil provides fluid pressure for the transmission to operate. It also helps to keep the transmission cool and lubricates internal parts. As the trans oil ages, it begins to break down and it loses some of its ability to perform these functions properly. If the trans fluid is allowed to run hotter than normal, this breakdown happens more rapidly and can cause premature wear and failure of the transmission. Many transmission problems stem from overheating of the transmission oil. A trans oil cooler assembly is like a small radiator for the trans oil. It serves to keep the trans oil at the proper working temperature to prevent this from happening.

How do Trans Oil Cooler Assemblies work?
On many vehicles with an automatic transmission, a partition in the radiator (where the temperature of the engine coolant is lowered) is utilized as a trans oil cooler. Trans oil is routed from the transmission to a matrix of tubes inside the radiator (but separate from the engine coolant). Air passing over the tubes cools off the oil before it returns to the transmission. But the trans oil in some vehicles needs more help than the radiator can provide. High performance cars, heavy-duty trucks, tow vehicles, or any others that constantly stress the transmission, benefit from a trans oil cooler. This component is usually a stand-alone unit, like a small auxiliary radiator, through which the trans oil circulates in order to be cooled down by air passing through.
What are the symptoms of a bad Trans Oil Cooler Assembly?
The most common problems related directly to a transmission oil cooler include leaks and blockages. If the trans cooler leaks and the fluid level drops, the transmission will not operate properly and the fluid temperature will increase. On some vehicles, low fluid can be checked with a dipstick. Unfortunately, many automatic transmissions today are not user-serviceable and have to be checked at a repair shop. Fluid leaks on the ground could also be a sign of a trans oil leak. If the flow of oil through the cooler or its supply lines is restricted because of a blockage, the fluid will tend to overheat. Overheated trans oil has a burnt smell that can sometimes be detected. It may also appear dark brown in color. If the transmission is slipping during driving, it could also be an indication of overheated or low trans oil. The transmission oil cooler assembly on some vehicles forces engine coolant from the radiator through passageways adjacent to the transmission oil lines inside the cooler. This style of cooler can be prone to allowing engine coolant to enter the transmission if an internal leak develops.