overheat.

I have not seen problems with the water pumps failing on these cars (some European cars have the water pump impellers fall of or fail but not the case with these engines). You hear the cooling fans turn on and off when the engine reaches higher temperatures, so the cooling fan and thermostatic appear OK. I would remove the thermostat and or replace it just in case it does not fully open. Does the engine over heat when it is left at idle for 15 or 20 minutes (ie no engine load) or is it when you drive the car for 15 or 20 minutes (ie engine under load). I wonder if the radiator is restricted? As you drive the car the temperature gauge should rise to about the middle of the gauge (slightly higher on hot days). As you drive under load the temperature gauge may rise a little higher (for instance climbing a steep hill) but rush air through the radiator should be responsible for cooling the coolant in the radiator at this point. As you coast down a long hill under no load you should see the temperature gauge needle fall 15 to 20 degrees if the radiator is cooling efficiently. If the gauge needle doesn't drop even slightly the radiator is probably restricted. Do you have to frequently top up the cooling system or coolant expansion tank? If so you may have a leak in the cooling system. There is a tool which enables you or your mechanic to pressurizing the cooling system and check for leaks. Are you loosing coolant due to overheating? Does the engine boil over? Finally coolant loss and over heating could be caused by a "blown head gasket". Hopefully not but to check for a blown head gasket there is a tool that checks for the presence of carbon monoxide ( a by product of combustion) in the cooling system. CO is only present if the head gasket is not sealing properly.