BMW Cooling Systems Maintenance and Service

The cooling system on your BMW plays a critical role in the optimal operation of the vehicle. When operating as it should, it's your best friend, but cooling system repairs can be your worst enemy when a component in the system fails or if you don't know how the BMW cooling system operates. The primary role of the cooling system is, in short, to maintain the proper engine temperature by cycling coolant through the engine. The coolant draws heat away from the engine and is then passed through the radiator to cool it with air. A thermostat valve regulates coolant flow, and your engine may be equipped with a temperature sensor which regulates external air cooling fans.

Your BMW cooling system consists of three primary elements, outlined below.

- BMW Hoses, Valves, Heater Core, Radiator and Expansion Tank

These components work in tandem to facilitate the transit and regulation of the coolant flow throughout the engine. Because of the types of materials used and their constant contact with coolant, these parts are more greatly affected by exposure time rather than how much they are used. Prolonged exposure to engine coolant results in eventual deterioration, therefore regular coolant replacements and periodic examination of all hoses and piping is highly recommended. When the engine coolant is drained and replaced, any hoses showing signs of wear should be replaced. We recommend that all hoses be replaced every few years as a preventative measure.

The radiator, heater core, control valves or expansion tank are normally only replaced or repaired if there is evidence of leakage or a blockage of some kind. These components should be evaluated by a BMW certified technician to ensure optimum performance and operational safety.

- BMW Thermostat, Fans and Radiator/Expansion Tank Cap

Temperature control of your engine's cooling system consist of the radiator cap, expansion tank cap, thermostat, sensors, fans and fan clutch. While these parts mainly function independently of the engine, they do impact engine control through communication with your BMW's computer system.

Essentially, the thermostat is a spring-loaded valve. The temperature of the coolant flowing through it determines whether it opens or closes. The thermostats include an electronic switch which can activate the check engine light, warning you way before there is an actual failure. This switch monitors the position and rate of the thermostat and sends a report to the engine computer. This helps with emission warm-up time and also gives you the best possible fuel mileage. If your engine temperature gauge consistently registers low, or starts out high followed by a drop to normal operating temperature, this could signal the onset of a sticking thermostat. Consult with a BMW professional immediately if your vehicle is exhibiting these symptoms.

Another important part of the cooling system which is either misunderstood or overlooked is the expansion tank or radiator cap, which, similar to the thermostat, is a spring-loaded valve which reacts to variations in pressure. If these caps need replacing, it must be an exact match with the same pressure rating as specified by the manufacturer. A radiator or expansion tank cap not intended for your vehicle should only be used temporarily in an emergency situation.

A belt-driven fan blade for pulling air through the radiator is usually on the water pump pulley and should have a fan clutch to control it. The fan clutch allows the fan to turn with the belt at low engine speed and "free-wheel" at higher speeds. A malfunctioning fan clutch might result in disallowing the fan to run at slow speeds (overheating in traffic) or disallowing free-wheeling at higher speeds (potential overheating on highway or reduced gas mileage).

- BMW Water Pump

The engine's water pump is the force behind the entire cooling system, keeping your coolant flowing. The primary water pump is belt- or gear-driven, but in some cases a secondary electric water pump is utilized to improve flow. Driving the water pump is the drive belt which turns it, however on some older models the pump and belt are external, running off the crankshaft pulley with a separate belt. Pumping system maintenance is essentially scheduled coolant replacement, drive-belt replacement and tension adjustment (for the external pumps). Beyond 100,000 miles, we recommend a complete replacement of nearly the entire cooling system including radiator, expansion tank, thermostat, hoses, belts and pulleys as a preventative measure. BMWs are excellent vehicles, however their cooling systems are notoriously unreliable and require extra care.