I am having an overheating problem with my A4. It was fine all day one day, overheating the next. So far I have changed the thermostat to no avail. The pump is spinning and not leaking or making any noise so I figured it had to be ok but am now questioning that. I have no flow through the radiator. and only minimal flow on startup through the heater core hose then nothing. I can get some flow by revving the engine but it is minimal. Can the impeller separate from or slip on the shaft? The car has 208K miles timing service with water pump was done at 177k. I was hoping the thermostat was stuck closed but the old one opened when I boiled it and no improvement with a new one. I am dreading doing the timing service, but have found much help here so it shouldn't be too bad. Is it possible to mark the belt and pulleys and if nothing is moved just replace the pump and slip it back together? I know the consequences if something DOES move, but was wondering if it was ever done that way.

 

Long as you index the engine properly, nothing should move - mark the belt, pulleys, and backplates behind the pulleys. I'm thinking the impeller itself isn't turning with the pump shaft. In any event, unless you have a blockage elsewhere, you're likely going to have to tear it down to see what's wrong.

 

I already had it most of the way apart to do the thermostat, but I was able to keep the timing belt on for that job. I know I want the large holes on the cam pulleys in toward each other and the timing mark on the crank lined up. once the belt is off how easy do the cams turn? If I mark everything in a few spots I would think I could get it back together the same but If it was that simple why would they sell a $180 tool to hold them?