Join Date: Dec 2005
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The cap keeps pressure in the system.If the pressure can escape,then this would lead to it overheating......BUT,if there is too much pressure,then the cap releases it(i.e headgasket problems).
You can check the thermostat by running the engine up to temperature,and making sure that the radiator and the top and bottom hoses are all hot.If the thermostat sticks closed,then the bottom hose will be hot,but the top hose and part of the radiator will be cold(and the temperature gauge will keep rising).
Just one thing,as the engine has lost some coolant from overheating,top it up and make sure there are no air locks in the system.If there are,then this could give misleading information about what the real problem is.
Good luck,and let us know how you get on.
I'd rather push my Alfa than drive a BMW....
Currently in Lagdti's garage:
2004 Saab 9-5 HOT Aero and a 2001 Audi A3 1.8 Turbo