Just because you have a late-model BMW 2002, don't think that you're immune from thermostat failure. Our 1978 BMW 320i with only 10,000 miles is a perfect example. The thermostat just decided to stay shut last night on the way home from the airport. Fortunately, cool air and interstate speeds kept the temperature down to a safe level until we could get home. This is a good reason to constantly check your gauges while driving and to be completely familiar with the normal position for each. A few minutes of inattention could prove to be extremely expensive.
How do you diagnose a bad thermostat? Well, if it's overheating, feel the top hoses. They'll be hot, hot, hot! The lower hose just below the thermostat will be cool. If your thermostat is stuck in the open position, it will take forever for the car to warm up and you will have a hard time getting any heat in the winter. All hoses will fee lukewarm.
BMW dealers are stocking a new-style Behr thermostat which can be identified by an aluminum support which is part of the casting when you look inside the lower opening. Also, on the outside ring at the upper end, the surface is .flat instead of the old rounded shape. These units are supposed to be superior and less apt to stick.
Whether your BMW is young, middle-aged or old, I heartily suggest carrying a spare thermostat, especially when on a trip. The "insurance" can mean the difference between an hour's delay and a day!
Author: Stan Simm