I just replaced the water pump, thermostat and coolant temperature sensor. After recently replacing the auxiliary belt tensioner and dampener, the increased strain caused the water pump bearing to scream.

I ordered a Bosch replacement water pump on Amazon.com for $60 and the other parts from mbonlineparts.com. I understood the price of the water pump when I saw that it was made in China. Is nothing sacred?

The instructions in the Haynes Manual call for removing the fan shroud, fan clutch assembly, the alternator and the whole water pump housing and then removing the water pump (and the thermostat assembly) with the whole unit off the vehicle.

I did not remove the alternator or the water pump housing. But, replacing the water pump and (especially) the thermostat with the water pump housing on the vehicle tested my patience. Both of the old parts were pretty nasty when I got them off. The seal on the thermostat was petrified.

Big lessons:

1) A Made in England Craftsman strap wrench ($15 at Sears) worked fine for holding the water pump pulley to torque the viscous fan clutch onto the pump assembly. MB's special pulley holding tool would have been $105 at a local dealer.

2) Removing the timing pointer (one bolt) and the belt tensioner assembly allowed me to get at all of the water pump bolts with a 1/4" drive universal joint.

3) The locating pins on the water pump are hard to get lined up. Going slowly, I lined both up at the same time and gently jiggled the water pump into place, but it took me quite a few tries.

4) There was what appeared to be a drain hose (?) on the bottom of old water pump. There was no mention of this in the manual.

5) If I had to do it again, I would probably go the remove the whole water pump housing route. It was really hard to hold the thermostat properly aligned in the housing and in place while installing the bolts into holes you can't see. The water pump itself was more straight forward. Going this route would require ordering the extra seal to refit the housing to the engine block. The water pump came with a seal to attach it to the housing.

I hope this helps someone out there thinking about this job.

Caleb

 

My wife's 91 300E has been diagnosed with a bad pump. Mechanic wants $260 parts and 5.4 hours of labor (but he says it's more like 6). Not really an option to DIM.

This forum says it's more like a 4 hour job and I can find the part for $100 on average online. Of course a cheap part that doesn't last is false economy, but on the other hand, $750!

Anyone have any longer-term experience with the cheaper replacement pumps? CCMcC, I'm assuming yours hasn't broken after 3 months?

 

Hi Tom,

The part is working fine. Since it was a Bosch part, I have been assuming that it would have been manufactured to Bosch's specifications and quality. The $60 price plus shipping on Amazon did make me wonder, but so far so good.

 

Thanks for the quick reply. another shop gave me a more detailed breakdown but hasn't seen the issue for themselves and their estimate was a bit higher. Maybe it's time for a new car...

 

Tom,

A Mercedes dealer quoted me $800 to repair the water pump. That is what led me down this path and the experience chronicled in the 1st posting.