"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
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
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.