BMW 840i Engine Oil Cooler Replacement Cost

An engine oil cooler is a small device that looks much like a radiator, works much like a radiator, and is mounted near the radiator. Air passing over the oil cooler will lower the temperature of the engine oil, and allow the engine oil to remain much more effective. This will prevent the engine oil from becoming too thin for normal operation.

This component is part of an extension of the engine oil system, where an oil feed line will constantly fill the oil cooler, and an oil return line will constantly drain that oil back into the radiator. While the oil is being passed through the oil cooler, it is being cooled because of tiny metal fins that are attached to the oil cooler core are in constant contact with flowing air, and since they are so thin they cool very quickly. This is a highly reliable and effective means of cooling engine oil which is hot from the process of combustion inside the engine. Especially during extreme operating conditions or with forced induction engines, the oil cooler helps maintain the viscosity of the oil, preventing oil breakdown and sludge buildup, and allows the engine to remain protected in the harshest of conditions.

Oil coolers seldom fail except for two main reasons. Leaks are the leading cause since the oil cooler is always under pressure and hot. The oil lines, seals, and oil cooler core will eventually wear out, and small perforations or seal degradation will take hold causing the oil cooler to need replacement or resealing of the oil lines. This will be obvious as an oil leak will be coming from somewhere other than the engine, most likely somewhere around the front bumper cover. Also, if the oil cooler cannot pass oil through the cooler core, the cooler will block oil from returning to the oil pan, and the check engine light will likely illuminate due to the knock sensor detecting clattering from oil starvation. Finally, the check engine light or oil temperature warning light will likely come on if the oil cooler is blocked by debris from the front, or if the fins on the oil cooler have become bent over the course of time. This, however, does not often require replacement, as there are specialty combs made to straighten and clean the fins on the engine oil cooler to restore functionality. Also note, a severely leaking oil cooler will illuminate the oil pressure warning light, as will a clogged engine oil cooler or engine oil cooler line.

Oil cooler failure is dangerous for the engine. The engine needs a constant supply of oil that has not been overheated, is the correct viscosity, and maintains its protective abilities. Viscosity and protective ability are crucial to the continued operation of any machine, and are directly related to the temperature of the oil. If the oil cooler is blocked, clogged, or leaking, the system has been compromised, and the engine is at risk. Immediate attention is necessary to help prevent future engine failure.

Engine oil coolers are most likely to be damaged in a collision involving the front of the vehicle. Due to their location, like the radiator and air conditioning condenser, the engine oil cooler is often one of the first components damaged when the bumper and bumper cover do not absorb all of the impact from a collision. Aside from collisions, an oil cooler system should not require replacement for several years, and at least 100,000 miles. This will decrease with lack of maintenance and severe operating conditions. The oil cooler lines will likely require resealing long before the oil cooler has a chance to fail.

When the oil cooler or lines have failed in some way, the technician will likely have noticed the check engine light, low oil warning lamp, low oil pressure lamp, or the engine oil temperature lamp. There may be several other checks before arriving at tests for the engine oil cooler, and those may include checking the reliability of the engine oil temperature sensor, the engine oil pressure switch, or the engine oil level sensor. If the sensors sending the warning messages are functioning properly, the technician will begin searching for the cause. If the oil cooler is leaking, it will be diagnosed and replaced right away. However, for oil pressure issues, the oil cooler may be removed and either backflushed or pressure checked to test for clogging. If the oil cooler and lines are incapable of passing fluid or air pressure, they will be flushed individually to find the location of the clog and remove it. For an oil cooler with bend fins, the fins will be straightened unless the technician does not believe the oil cooler can be salvaged.

Replacing the oil cooler involves removing the mounting hardware or fasteners, disconnecting the two lines from the oil cooler, and installing the new oil cooler in its place. Afterwards, the engine oil system will be flushed, drained and refilled with clean oil, and the oil filter will be changed as well. For oil coolers which may be part part of the vehicle's radiator, the engine cooling system would be drained, radiator removed, and the cooling system would be refilled and bled after the repair is complete. Lastly, the technician would drive the vehicle, monitor oil pressure and temperature, and possibly manually clear the OBD trouble codes before confirming the repair.

Removing the oil cooler in an attempt to prevent a repair is not recommended. The oil cooler can be bypassed in order to avoid towing the vehicle home, but any sort of strenuous driving may cause excessively high engine oil temperatures. If there is trouble with the oil cooler, and it no longer functions properly, replacement is the safe option.

Many vehicles do not have oil coolers, and many radiators have two cores to accommodate engine or transmission oil along with engine coolant. In any case, it is important to understand the system used on your vehicle before authorizing or performing maintenance to the engine oil cooling system, as there may not be one. Also, power washing any air to liquid cooler will cause the fins to flatten, which blocks airflow and reduces efficacy of the cooling unit. If cleaning is needed, a radiator comb is the tool for the job, and lightly pressurized water can be used in a non-dusty environment.

Diagnosis of a clogged engine oil cooler will be a little more difficult, but a blocked or leaking engine oil cooler can be diagnosed by anyone, and the radiator comb available to straighten fins and removed debris is consumer available at most parts stores. A leaking engine oil cooler can be replaced at home with a quality set of line wrenches or quick disconnect tools, depending on the make and model. The beginner DIYer could accomplish this task with a little assistance as long as removal of body panels is not required to access the engine oil cooler.