In the winter, when the outside air temperature decreases, the BMW 2002 thermostat does not function well because it is detached from the engine block and directly in the path of air flowing through the radiator.

Instead of wrapping insulating material around the thermostat (which is not easy to do) or attempting more complicated solutions, try this: In the fall, when the outside air temperature drops to about 45-50° F, simply remove the front grill and block off the left side of the radiator by wedging a piece of cardboard (at least 8.5″ x 11″) between the radiator and the surrounding body metal.

The effect in lowering winter engine temperature is quite dramatic. The radiator must be unblocked in the spring by removing the cardboard, because leaving the radiator blocked in the summer will cause the engine to run hot. You will know if you have installed the radiator blockage too early because it will have the opposite effect (i.e., a rise in temperature).

It is also interesting to note that as engine speed (road speed) increases, engine temperature will decrease with an unblocked radiator (summer) and increase with a blocked radiator (winter).

Author: Louis A. D’Amario