Overheat Question

[Mauritius36]

After about a 50 minute drive today, the car was parked but still running for about 5 minutes. When I got back in to park it and turn it off, I noticed the temperature guage was all the way in the red. Im sure it was not there before I got out. I immediately turned the engine off and opened the hood up. The only thing I noticed was a hissing sound coming from the region around the coolant reservoir. Also, within 10 minutes of turning off the engine, the temperature guage had returned to its normal center position. I would appreciate any suggestions as to what the cause could be, things I should check on, or how I should proceed in general. Thanks

[I3MW]

I would say the clutch fan.

Check that your aux fan turns on (both relays) and the clutch fan for some mechanical resistance. It's hard to gauge wether the clutch is good or bad so I say if it's original replace it. It's always neglected on the E36 because it's and relatively expensive part and doesn't always have an obvious failure. The hissing is probably because of the pressure in the coolant system and the coolant reservoir can be the weakest link. Make sure you don't have any leaks. How's the car doing otherwise man? Still got that exhaust?

EDIT: if you need the clutch fan tool, let me know.

[RuninDawg]

Check the electric fan(aux fan) and the mechanical fan clutch. How many miles on water pump/thermostat? Those could be at fault as well. Sound you heard was venting from the reservoir cap since the system was overheated/over pressurized.
If you were in the red on the gauge, fairly good chance that you have(or will have shortly) problems from head gasket sealing/head warpage.

[Mauritius36]

Cant the car function without the fan entirely? (weather was cool btw) Only reason I wouldnt think thermostat is that it only happened when the car was sitting. I have somewhere that I need to drive this week (about an hour each way). Would you try to avoid using the car entirely for now?

[RuninDawg]

Until you figure out why you overheated, I would absolutely not drive the car.
You risk a head gasket job(at best) or a ruined engine(at worst). These engines don't like to be overheated at all. You can search if you want to read the many tales of woe.