Car overheats with no CEL or coolant leak

[anaElBasha]

The car drives fine but I do notice usually when I’m on idle for a few minutes it would overheat with a red warning saying to stop driving now. I’m assuming it’s my AUX fan or my radiator but I have no idea how to confirm, any idea? 06 750li

[jclausen]

Until you do a proper diagnosis and check for stored faults who knows what's happening

[anaElBasha]

Already ran diagnostics and didn’t show any faults in regards to this issue. I did run the AC and check under the hood, my AUX fan wasn’t running.

[jclausen]

Since the fan gets its signal from the dme I believe some body needs to figure that out

[anaElBasha]

Do you mean it doesn’t report it on the report? It was diagnosed with one of those $400 diagnostic tools that reads more than just basic codes

[AuntJemima]

Could be radiator fan clutch, simple fix you can do yourself. I had it happen on a e36 325i. My symptoms were car would overheat (temp gauge moving towards red) when idling or very slow driving in the city. As soon as I got on the highway / open road moving 40+ mph it would cool off and temp gauge would go to normal. You can test by sticking a few pieces of rolled up newspaper into the fan blades when the car is operating temperature and running. If the fan clutch is broken, the paper will stop the fan. Fan clutch is not expensive, it just requires 2 wrenches to remove, if you can change your oil you can do the fan clutch. I am not an RKI and my advice could maim or kill you (disclaimer).

[MJeffC]

I think you already know the answer. If it only overheats on idle but not while driving then it definitely is the aux fan. It is PWM and full voltage will not trigger activation. Turn on the AC, the aux fan should run. Check the plug on the side of the fan for 12V, unlikely but it might also be the fuse. You can also put a scope on it to see if it is a square wave.