So I have a similar, yet different problem. Hear me out here, and please help!!!
I have a 2000 BMW 323ci with about 90K on it. I was driving the car normally at 60-70 km/hr for about 20 mins and happened to look at the temperature gauge and the needle was way over on the right at the end of the red zone (see pic below). There was no heat coming from the vents, and the interior of the car was ice cold. I wasn't revving the engine or doing anything out of the ordinary except driving in the city. I drove for another 5-10 mins to get home and shut the car off. Mind you the weather here in Canada is at -20C (-4F)...
The next day I brought it to a local mechanic who said that the problem was a busted thermostat that was stuck closed. So after $280, he apparently replaced the thermostat and changed the coolant, and then sent me off.
The next day, I started the car and let it warm up for about 3 mins or so before driving, and within 10 mins the same thing happened again - needle goes straight to the red zone and stays there. No hot air coming in from the vents. I pull over immediately, shut the engine off, let it cool down for 5 mins. And then started it again, this time letting it idle for 8-10 mins before driving off. Then I proceeded to drive for 30 mins, and everything returned back to normal. Needle was a little past the blue/cold range the entire time, and there was hot air coming in (interior temperature is set to 23C (73F).
I decided to bring it into Europa Motors to get a second opinion (accredited independent BMW service providers). The mechanic said he couldn't find any problems except maybe the thermostat signal/computer had to be reset, but noticed it was strange that the coolant was white coloured.
So off I go again into the car, warming it up for 3 mins before driving off. Then within a few minutes, the same problem re-appears. Needle goes to red zone. I turn around and bring it back to shop to show them, and all of them are scratching their heads. Now the car is in their shop until Monday before they can do a more detailed diagnosis.
Anyone have a clue as to what's wrong here?