Auxiliary Water Pump

Save your money for more important repairs.

Perhaps you don't need it at all. If it's not gushing just unplug the motor it and see how well the heater works without it.

I found there was no heater performance difference, removed the pump and substituted a 1/2" copper 90 degree turn and short piece of copper pipe for it.

I am not sure for your particular model.

But for the later engine (104) the auxilliary water pump in normal operation of course ensures circulation through the heater core, but it also ensures circulation of the entire engine cooling, after engine is switched off, to avoid hot spots and the formation of vapor bubbles.

"Perhaps you don't need it at all. If it's not gushing just unplug the motor it and see how well the heater works without it. I found there was no heater performance difference, removed the pump and substituted a 1/2" copper 90 degree turn and short piece of copper pipe

for it. "

I'd love to know why they ever put these aux pumps in to begin with. The motor went on mine in my 80 300SD and like TG, I haven't noticed any difference in heater performance. The only scenario where I think it might make a difference is when its cold and you start the car and leave it idling instead of driving off. Then, at low RPMs I think it might get heat to the cabin faster, but I've never tried it to find out.

And beware of the replacement ones that people are selling on Ebay and elsewhere. If you do want to replace it make sure it's a Bosch or similar quality manufacturer. I bought a couple from Adsit Company and they were China junk, only lasting a few months before leaking.