Ursprünglicher Beitrag von: Nicolas Siemsen ,
These pumps are made of solid cast metal and are rather durable. The most common failure for these water pumps is that the internal seal begins to leak. Water will then drip out of the weep hole in the side of the pump. As long as your pump is not leaking and your are not having any overheating issues you do not need to replace it. The procedure is: Start by draining the coolant from the radiator and block. The W123 page on this site has instructions for this under the coolant change guide. Remove the belt(s) for the alternator/water pump. To take it off you will need to adjust the alternator so it moves closer to the engine block. You can find instructions for adjusting the alternator to remove/add belt tension online. Once the belt is off, you then need to remove the fan and clutch. The fan clutch is attached to the water pump with four 10mm bolts. Removing them is tricky but can be done with patience. I always advise ordering several new bolts from Mercedes before doing this job in case one rounds off. They are bolts not readily available at your local hardware store. With those four bolts removed the fan and clutch can be taken out along with the fan shroud, which is held in place by two clips. With the fan, clutch, and shroud out the water pump pulley is readily visible. It should pull off the pump but may be held in place by a bit of rust. If so you can tap it a rubber mallet. Once the pulley is off you proceed by removing the six 10mm bolts that hold the pump to the block. Go slowly, backing the bolts in and out if they get tough to turn. Be patient and do not turn the bolt with a lot of force as they can sheer off leaving you with no option but to drill out the bolt. After those bolts are out the pump can be pulled from the block. Clean up the surface where the old gasket was, then install the new pump with a new gasket coated with a bit of aviation gasket sealer (do not use silicone or RTV sealers). Let the gasket sealer cure for a few hours, then you can reverse all the above steps. Finish by refilling the system with fresh coolant/water mix as shown in the coolant change guide.