About 6 times in the past 12 months I have found my temp. indicator going into the red. I have replaced my radiator, fan clutch, thermostat (two times). The car has 125,000 miles and I do not believe the water pump has ever been changed. On my last trip at about 250 miles into the trip on the highway without much stopping with the outside temp at about 20 degrees it occurred again. A local garage changed my thermostat (I later tested this thermostat in boiling water and it did open). They found that the bottom hose was not very hot. My return trip was fine, same outside temp. with much heavier traffic. Heater does smell like antifreeze when it is first turned on but smell goes away. Heater gurgles sometimes when it is turned on. BMW dealer last month could not find the probem on the pressure test. (I am not sure how hot they got the engine) I do have occasional minimal leaking of antifreeze on the floor but not so much that I am adding antifreeze. I suspect that air is getting in somewhere causing an air bubble and blocking the flow. Help.