Hey everyone. I'm new to the forums and I'm really looking for some advice on where to start with my issue. I have a '97 528i with the M52 engine, 170k miles. A month ago I began to have an issue with my temperature reading. I had absolutely no control over it and just recently purchased the vehicle. I went to have code read for testing and the "problem" went away for over a month before returning even worse than before.

When test #7 is displayed on my cluster, the engine starts cool and warms up like a typical vehicle. However, the needle reaches the center of the gauge (supposed to be about 90-100°C) when it reaches it at a sensor reading of about 70°. It will reach 100 and surpass it if the car is still running, typically passing 115 or 120° before either stopping or spiking up to 130°, where by now the needle is holding in the red. It does so for no more than a minute before quickly dropping back down to 100. It then will slowly make its way back up and repeat as it continues to run.

I have narrowed down the most likely issues, but I really don't want to fix them unless I know what the most likely problem is:

-a bad temperature sensor. There are too many of them and I don't know which one actually controls the gauge on the dash. The internet has been unclear to me.

-an intermittently failing thermostat. Staying closed normally then refusing to open before finally opening and quickly getting stuck again.

-air bubbles in my coolant system causing the sensor to spike. I have a very small coolant leak from some hose but it is too cold here to bleed it as of now. But I'm afraid if I don't resolve this I will blow an engine and be out thousands.

Has anyone else also had this issue? I'm really hoping to repair it. I love the car. 5 speed close ratio manual. Rare and fun. New clutch and solid on the road. I appreciate the time taken to read this.