In 2006, I bought a certified 2004 BMW 325xi. After about a year, the cooloant light came on, and the BMW service manager said this is common on this vehicle. Hew said just top it off which I did. Is there a bigger problem he is not telling me about. There are no leaks.
BMW 325 xi coolant level. on 2004 BMW 325i
The cooling system in any car is a sealed system and shouldn't really require frequent topping up. I would suggest having the cooling system "pressure tested" if the level falls again. To pressure test the cooling system the filler cap is removed and the system is pressurized with a device that is similar to a bicycle pump. With the system pressurized the cooling system is inspected for leaks. BMW do have some plastic housing that deteriorate with age and heat cycling.