1990 e 30 motor 325I model overheating

Answer 1

air in the system.... bleed the cooling system. f you didnt change the coolant before the problem started then u willl have to look for tiny leaks... some of them are noticeable only when engine running (Water pump for instance). thermostat is possibility too, and then the fan clutch is another one too... the last big major reason would be the heafd  gasket.