Auxiliary Water Pump

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scanham - 24 Oct 2005 18:27 GMT

My 1987 300E has a leak in the cooling system that appears to be coming
from the Auxiliary Water Pump. I understand that this is used to pump
water into the heater core during engine idle. I called the local MB
dealer who quoted me a price of $357.50. I found a new one online for
$118.69 which looks very similar but says that it is for Chassis: Up
To: B 527022. My Vin is WDBEA30D3HA357927 - the last 6 digits
indicate chassis, right? I asked the online store and they said it
would not fit, but I'm not sure if they are correct and I am tempted to
try it anyway. What do you think?

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Martin Joseph - 24 Oct 2005 20:53 GMT

> My 1987 300E has a leak in the cooling system that appears to be coming
> from the Auxiliary Water Pump. I understand that this is used to pump
[quoted text clipped - 5 lines]
> would not fit, but I'm not sure if they are correct and I am tempted to
> try it anyway. What do you think?

Save your money for more important repairs.

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Jens - 24 Oct 2005 22:00 GMT

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.

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T.G. Lambach - 24 Oct 2005 21:35 GMT

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.

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trader4@optonline.net - 25 Oct 2005 17:41 GMT

"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.

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