2015 BMW 335i GT xDrive Trans Oil Cooler Assembly Replacement Cost

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.

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.

Transmission problems are often considered to be some of the most dreaded and costly repairs on a car, truck, or SUV. It is important that, if the transmission is slipping, it be evaluated as soon as possible. If the trans oil level is low, fluid should be added as soon as possible and the vehicle should be checked for leaks. And if high trans oil temperatures are suspected, the vehicle should be serviced. Transmission problems do not tend to resolve themselves. Driving for significant amounts of time will usually result in increased damage and more expensive repairs.

A trans oil cooler assembly should last the lifetime of a vehicle. Regular maintenance, including transmission oil changes at the manufacturer's recommended intervals, will help preserve the life of the cooler.

There are many problems that can arise related to a transmission. Some of them can stem from a bad trans oil cooler assembly. But to diagnose the assembly itself, a technician will first check the trans oil level. Then the vehicle is lifted and supported to gain access to the cooler assembly. The cooler and the supply lines are checked for leaks. A technician may flush the lines and the cooler assembly to make sure there are no blockages present that might restrict the flow of trans oil.

If the trans oil cooler assembly is damaged and leaking, or if it has an internal blockage that prevents oil from flowing, it will be replaced. To do so, the technician will drain the transmission oil. Any accessories that are in the way of access to the cooler assembly are removed. On some vehicles, disassembly can be significant. The supply lines are disconnected and the assembly is removed. With the new cooler assembly in place, new seals (and maybe new supply lines) are installed and fresh transmission oil is added.

RepairPal recommends replacing the transmission oil filter at the same time that the trans oil cooler assembly is being replaced. Trans oil changes should be done at the manufacturer's recommended intervals as part of routine maintenance.

A problem with a trans oil cooler assembly - especially one that relies on engine coolant circulating through the assembly - may be difficult to detect when there is no trans oil dipstick. A trained technician should perform a thorough inspection of the system.

Someone with intermediate to advanced DIY experience could replace the trans oil cooler on many vehicles. Access to the component varies. Accurate diagnosis, however, is essential to preserve the life of the transmission.