On my 300d 1985 the electric water pump is not working. Is it supposed to run all the time, or just when needed, if when needed what controls it? I did put power directly to it, and still will not run, so expecting that I need a new one, however want to know how much it is needed, and what controls it. This is my first Mercedes, and just getting it fixed up. It does run well, and the body has little rust.

It is controlled by the climate control system. It improves heater flow at low engine rpm. It should operate only when the heater is operating. You can get by without it, but I would disconnect it unless/until it is repaired.

depending on where you live and/or your tolerance for low temps, you can remove it and replace it w/ a plastic elbow. I done it on 2 cars and never noticed a difference.

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Cheers,
Robert

ok think I will bypass it for now, and see if I get enough heat this winter. Thanks