Porsche Repair: Porsche 928 Heating Problem, radiator tanks, crank pulley

Question
Hi there Dave.I 've just purchased a 1980 928 Porsche.The radiator tanks was cracked so I had new aluminium ones made up & fitted.Problem is that the vehicle is overheating.Already checked & tested for gas in the water system, it was clear.Thus couldn't be headgasket.It seems that there is little or no waterflow through the radiator.I suspect maybe waterpump but don't know.Your info on this will be highly appreciated.Also, can you perhaps help me in locating the water pump location on the engine...

Answer
Hi Neil,

Let's start with the easier question first.  Find the water pump by tracing the radiator hoses back to the engine.  The typical set-up is that the radiator's lower hose will connect with the water pump's lower connection (the hardest one to actually see) and the upper hose will connect to the engine block where the coolant will pass through the thermostat and then into the water pump.  The obvious clue is that the water pump will always be positioned so it's pulley is directly over the crankshft pulley.   The crank pulley is typically the largest and widest and lowermost pulley located at the engine's centerline.

Cooling problems can be caused by many gremlins.  If you suspect the water pump, there are two symptoms to look for.  Usually the front bearing in the pump will be squealing...and the true test is simple:  Idle the engine and watch the temp gauge rise toward "normal" operating temperature.  When you start this test feel the upper radiator hose and it'll be cool (not hot).  At some point close to normal operating temperature the hose will change from cool to too hot to handle.  If it does, water IS circulating through the radiator.

This happens because the thermostat has engine coolant knocking on it's door, wanting to get to the radiator.  But the themostat prevents this transfer until the coolant in the engine rises to "normal" (let's assume 180 degrees F) and as soon as it does the thermostat allows coolant into the radiator to keep the temperature from rising further.

Check this out and let me know what you find.

Dave