Hello all! I have a weird problem with my wife's 04 X3. Lately the coolant light has turned on. There are no leaks, I have checked and so has a mechanic, and no check engine light. The coolant is full, and the light turns on and off at random. But, the system is blowing cold air even when on heat. Another thing is the temp gauge stays perfectly upright, and never wavers.

So I had several ideas of what could be wrong. Is it one of the sensors? Or, a more expensive option, the thermostat?

This engine is obviously very similar to my e46's engine, and I have the tools and know-how to repair the cooling system if I need to. I just do not want to go ordering parts if all I would possibly need is a little sensor.

Thank you all for your help! My wife will be happy to have heat when driving around in this cold weather haha. This site has been awesome, I have already used the DIY to repair her GPS