Lou,
I drive a 2002 BMW 325CI - I have had this vehicle since 2007 and treat it with the respect it deserves. It remains in near mint condition and with only 164,000 kilometres on the engine. I look forward to many more years of driving pleasure. However, a number of years ago during a winter drive to visit my sister about five hours away, the heater started to provide only cold air. This occurred after about 45 minutes on the highway - the ride back home was rather chilly indeed.
This happened again before I took the car into my local BMW dealer to get to the bottom of the problem. On this occasion and a second occasion as well, they could not find anything wrong with the heating system. I don’t drive the car much in the winter, but trips around my city are fine as the heater works as it is supposed to. On the other hand, I have not taken it on winter highway trips for a couple of years now. Do I have to take a dealer technician on a long drive to ‘prove’ the problem exists? Any advice you can offer will be greatly appreciated. - Bob D.
While it may be obvious to many of you reading this is, there are also many not familiar as to where the heat in your non-electric vehicle originates from. The engine produces a lot of heat and requires coolant to facilitate removal of that heat via the radiator. A small portion of the engine’s coolant is routed into your dash where another small radiator known as a heater core also provides a heat exchange into the cabin, warming the occupants.
Firstly, the coolant temperature needs to be verified. An engine thermostat can sometimes randomly get stuck wide open. When this happens, the coolant will be constantly routed to the radiator, subsequently removing too much heat from the coolant and the engine will run cold. If the engine is running cold, then your heat inside the cabin will also cool down, especially noticeable on longer highway drives. The next time you go for a drive, note specifically where your temperature gauge needle regularly points too. When this lack of heat situation occurs next, check to see if the gauge is showing a lower-than-normal reading which would indicate your engine is running cold.
Secondly, your BMW uses an electronic heater control valve. This is a control flow valve that will open and close a small coolant passageway feeding the heater core. If the electronic portion of the heater control valve fails to do its job, then no hot coolant will be routed into the dash. No hot coolant means no interior heat. Shutting the car off and restarting it will sometimes reset this flow valve and it will once again start working normally. These valves are commonly known to fail intermittently on many BMWs from that generation. If I had to guess, I would say examining this flow control valve presents the most likely chance of sorting out your issue.
Lou Trottier is owner-operator of All About Imports in Mississauga. Have a question about maintenance and repair? E-mail globedrive@globeandmail.com, placing “Lou’s Garage” in the subject line.
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