BMW Cooling System Information: Troubleshooting and Tips for older BMW Cars

The single best instrument for testing your older BMW's cooling system (radiator, fans, thermostat, water pump, hoses etc) (E9-E36,roughly) is your BMW's temperature gauge. Learning how to read and understand the temperature gauge is underrated and less common knowledge than you might guess. In southern climates, the cooling system found on older BMW's is marginal on hot, humid rush hour days when the AC is even ineffective. First off, do not open the cooling system unless the temp gauge is showing halfway or less. Avoid potentially serious burns this way. BMW Engine coolant: The best coolant for old school bimmers is 100% water. However, water freezes and rusts the engine block. The compromise is to run a 50/50 mix of antifreeze and water. Not only does the coolant mixture need to be right, but so does the coolant level. All six cylinder BMW cars have coolant/radiator expansion tanks, all but the earliest of which have a 'max' level mark indicator. No mark on your (old!) BMW? Fill it to the tank seam. You can leave the condition of your cooling system to chance and to the warning lights if your car is so equipped, but I say periodic hands on inspection is needed. Most (pre M42, ie M10 engine cars) fill directly at the radiator, making coolant level harder to figure out. Coolant MUST be higher than the top of the core and it usually ends up about halfway between the core top and radiator cap. Not sure of the level in your car? Fill the radiator to the cap, take the car for a test drive to bring the system up to operating temp, and the system will bleed itself of enough coolant necessary to create the air pocket for expansion. This gives you max amount of coolant and the space needed for hot coolant expansion. Temperature gauge needles usually hover around the midpoint on most BMW's during normal driving. Extreme outside temperature conditions vary needle positions slightly. The hotter and more humid the weather, the less efficient outside air draws heat from the radiator. This increases coolant temp, and makes the needle tick slightly upward. The engine idling for extended period in hot weather (especially with the air conditioning on!) can bring the needle to the 3/4 mark. If it is really hot out, your best bet is to shut off the AC and crank the heater fan on the lowest non AC setting to prevent the engine temperature from going into the 'red' area. To be continued: The next segment will tackle Troubleshooting and diagnosis, plus cooling system maintenance tips.