I have a 97 bmw

Thermostat stuck?

You actually need the thermostat in to pressurize your cooling system or the coolant won't cyle through the radiator, it'll just cycle around the engine. Most people think without the thermostat in the coolant will just pump freely through the engine and radiator, but it doesn't.

Chuck in a new thermostat, purge the air out of the system and see if it overheats then. I gaurentee it won't, if it does then you've got head problems (but they should already be obvious by now).

i have a bmw 318i auto 1998 model, ive changed the water pump, the radiator, took the themerstate out, put the fan on direct, & had the head gaskit checked & still it overheats when driving after 10 minutes. the temputure shoots up suddenly. please help me cure this problem. thanks.