E83 Overheating / Bleeding Issue or what the heck is going on?

[dragonblue24]

Hi Folks,

I had some loss of coolant and it looked like it was the upper hose that connects to the expansion tank.
So I got a new hose, bled the system (cold engine, key to second position, heat cranked up and top off until it comes out of the bleed screw) and thought I was done.

But after a couple of days it started overheating, needle moving rapidly into the red and by the time I pulled over it would often come back down to 3/4. So I thought there must be an air bubble in there some how and I bled it again. I watched various YouTube videos on how to bleed it, parked it uphill, etc., etc. but it still does the same.

The only time it stays more or less on the 12 o'clock position is when I leave the heater cranked up. Then it stays pegged like it should (even under load) but as soon as I turn off the heat it overheats. And again, the needle moves pretty quick, it's not a gradual increase. Oh, and it's not the fan, that seems to be blowing fine.

At this point I start having a hard time believing it's an air bubble given how often I've bled that beast. But maybe I'm doing it wrong somehow? But then why is it fine with the heat on?
Or maybe it's something else altogether like a temp sensor? Partially clogged radiator? The thermostat? Demonic possession?

Does anybody have some 2 cents to share on that before I in no particular order lose my mind, start tearing the whole thing apart, throw new parts at it and/or call Ghostbusters? Or rather what should I tear apart first and how much is an exorcism?

Thanks in advance for your help!

[my1stE30]

Possibilities might include:
- head gasket leak allowing a small amount of exhaust gas into the coolant system (even if the oil is not affected yet)
- partially clogged radiator or partially blocked radiator hose somewhere
- thermostat stuck in a partially closed position

Good Luck and hope those comments help a bit

[dragonblue24]

Thanks that does help a bit, I kinda doubt the head gasket because that would also happen with the heater on, wouldn't it?
It's somehow not cooling enough which is why with the heater full blast it works fine.
I think I might try changing the thermostat... Maybe I can first inspect it...


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