Reoccuring coolant issue

[JetMech]

I've been so frustrated over this. I got a new radiator because of a previous problem with air in the coolant system, that thread is linked so you know what happened if it would matter. New radiator on and my car keeps saying check coolant level. Whenever I pop the hood, the tank is full of coolant except once. That day was 20 degrees and in the morning but I have no idea if that matters, I'm just talking out of my ass. I'm not losing any on the ground and I'm not finding any in the engine. Does this sound like a sensor or a real problem? I'm no car mechanic, I'm at my wit's end. Thanks for any help anyone can give.

http://www.bimmer.info/forum/showthread.php?t=28145

[Michael999]

the sensor is right on top of the tank, it beeps if its not submerged in coolant.
its directly behind the coolant cap.

sounds like a dead sensor, take it out and give it a clean, if it still happens get a new sensor.

[DaveVoorhis]

If the tank is full, it's a sensor problem. It being empty (or just low?) one day is a bit suspicious, but if it wasn't bled fully it might have been working the air out.

The sensor is at the bottom of the coolant tank, with the electrical connector under the rad on the left -- assuming your 525i is like mine and has the tank on the side of the rad. The electrical connector might be loose, disconnected, or the contacts corroded. It's also possible the folks who changed the radiator damaged the sensor when moving it from your old rad to the new one. It has a float that pops off easily if the sensor isn't removed carefully, and it might have been left behind in the old rad.