Volkswagen CL Umwelt TD Estate. 1.9 AAZ engine 1998 S reg.
New waterpump, still overheating, the blower is heating up just fine and all hoses hot except the bottom radiator hose. What next? Airlock , or thermostat. I'm guessing it's an airloack as the first overheat was the day after the coolant was renewed. The second overheat was after the new waterpump and again renewing the coolant.
Feel the Upper Radiator hose as the engine starts to warm up. As it starts to get hot see if the radiator is hot at the upper corners. When the temperature gauge gets to midpoint the thermostat should open up and the radiator should begin to get hot. The temperature gauge will drop slightly and the start rising again until you hear the radiator fans kicking on. If the temperature keeps rising and rising and the fans don't come on then I would suspect the radiator fuse, the radiator fan sensor in the radiator or the radiator fan module if applicable. The wiring could also have a problem possibly even corroded near the battery. You could power the radiator fan by supplying it with power and ground, and it might have 2 speeds.
If the radiator does not get hot then I would suspect the thermostat or a blockage of the hoses.
If the radiator gets hot and the fans come on then I would suspect something blocking the air flow through the radiator or internally clogged passages inside of the radiator. I have seen one vehicle, not a VW, where someone wired the radiator fan backwards and instead of pulling the air through the radiator the fan was pushing the air through the rad to the front of the vehicle. It was overheating too while driving! ;-)
I think you mentioned that your vehicle does not have A/C so you can't turn that on to see if the fans work. :-( BTW I have replaced more rad fan modules than rad fans, but I am not sure what your vehicle has.
Save yourself the year long headache I suffered, check the coolent system pressure cap, make sure it is holding the proper pressure, they are usually cheap anyway so just outright replacing it is not unrealistic (and hardly anyone ever thinks of it, even VW shop mechanics)
------- Because you are having problems with both the overheating and keeping a good charge in the battery I'd suspect you have problems with v-belt tension. Maybe loose mounts on the alt. or p/s unit.
Thank you all very much for the replies, I will check it out tomorrow, I should have done it today but I was out with my partner in his cavalier (diesel) when the timing belt broke, camshaft on that one is a gonner :-( So twice as urgent now for me toget mine sorted. It never rains but it pours :-(
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