Engine Cooling problem
1994 BMW 318 4 cyl Two Wheel Drive Manual 140000 miles
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i have a BMW 318i thats overheating. I put new thermostat and water pump in it but it still overheats? How do i avoid getting ripped off by a mechanic by eliminating (doing small tests myself) so I know they are not charging me for the wrong "big issues"?

It is possible the radiator is the culprit here, has it ever been replaced? When is the over heating happening? After a drive, during a drive while in traffic, just sitting there idling or ?

I know this is a silly question. Is the system full with water and coolant? My friend recently replaced his coolant system and filled up the system with engine off. He thought the system was already full and overheated after driving couple of miles.