What is this pump on '86 300E - PeachParts Mercedes-Benz Forum

plink49 · #1 02-17-2004, 08:08 PM

The attached picture shows a pump/motor below the coolant expansion tank on an '86 300E (pink circle). It is obviously something to do with the heater, but what, exactly? There is a gasket between the pump halves (yellow arrow) that is leaking coolant somewhat profusely. Is this gasket available as a separate part, and if so, what is the part number?
Thanks

porkface · #2 02-17-2004, 08:27 PM

it is the aux. water pump. supposed to provide heat while the engine is idling. no parts available, replace the pump. good luck, chuck.

pfphipps · #3 02-17-2004, 09:04 PM

Or you can just take it out and tie the two ends of the hoses together. I had one start leaking on a fairly new MB while skiing in Utah in the dead of winter. I put piece of fiberglass tube in until I got home and it could be fixed under warranty. I know it is supposed to help provide the heater with hot water at idle but to tell the truth, I could never tell the difference even at the below zero temperatures I experienced at the ski areas.

pesuazo · #4 02-17-2004, 10:29 PM

I removed the pump, remove the 2 (or 4?) phillips heads and sealed the 2 surfaces with RTV sealant.
2 hours, and I took my time.
No leak for the last 6 months.
I have read of success stories fixing the pump if it is not working. Do a search.
Keep us posted.

cornblatt · #5 02-18-2004, 11:42 AM

This is an electric coolant pump, controlled by the climate control system, that will pump hot coolant through the heater core inside the car. It is intended to provide better heating for the passenger compartment, especially when the engine is idling (at which time the car's mechanical water pump isn't turning very quickly).

My auxiliary coolant pump was leaking a few weeks ago too, just as you described. A new pump was quoted at $130 to $180 (parts only) depending on where you buy it.

I replaced it with a copper PEX elbow pipe fitting (available at Home Depot for around $1). It fits perfectly, and has nice ribbed ends to make sure it stays in place. I didn't even have to drain the coolant from the car to replace it - just clamp off the hoses on either side of the pump with vise grips to stop major coolant loss, and then quickly pop out the pump and replace it with the elbow pipe fitting. I only lost about 3 cups of coolant in the process.

So far, I have noticed NO DIFFERENCE in the climate control system operation - the car heats up just as fast as before (and it's been cold here, -20°F), and the hot air is just as hot as always. So, no more leaking coolant, no loss of performance, and a lot of money saved...

I intended for this to be an interim fix until I could find a more economical replacement pump, but given that there's no loss in performance whatsoever, I think I'll keep it as-is.

If you're on a budget, note that this type of pump is used on a lot of other german cars (VW, BMW), so if you're desperate for a replacement pump, you could find a similar non-Mercedes replacement at an auto wrecker and just solder the MB connector onto the 'new' part so that it fits in your car.

cornblatt · #6 02-18-2004, 11:42 AM

Here's a picture of the PEX elbow fitting...

guydewdney · #7 02-18-2004, 01:23 PM

do you guys have a 'rest' button on the climate control to allow the heater to keep working with the engine off? if so - is this pump spposed to feed this?

plink49 · #8 02-18-2004, 09:07 PM

Hey...thanks guys for the replies! Since the pump actually is working and it's only the gasket I think I'll opt to go for the disassemble quickly and reseal the pump with form-a-gasket or similar. If you are in Alberta, Cornblatt I doubt I would have a problem down here in the southwest, New Mexico! But, if the form-a-gasket doesn't work I'll go with the copper tube bypass.