I am getting cold air at idle while heater is on. I searched and the probable cause is the aux water pump. Questions:

1. How to test if pump is dead? Will injection of 12v run pump?

2. How to install new pump? I see a bracket attached the car body frame that holds the wide rubber that grips the pump, do I take this bracket off?

Thanks for any input.

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joel

Prayers bring forth enlightenment.

Unless you live in Gnome, Alaska, I'd bet the problem is elsewhere. The aux pumps are notorious for dying in place, and you never really notice it unless you're in a seriously cold place. Mine was dead for over 4 years on the TE and we always had heat. My 1980 300D had crappy heat, but that was because I had crud in the heater core that I was never able to flush out. The aux pump on that car never worked the whole time I owned the car, so I know that wasn't the problem.

HTH,

someguyfromMD

Up here in Boston you notice real quick in winter if the Aux Water pump is gone.

On my 190E it was a simple 20 min fix, unbolt and rebolt with the replacement.

You could test by removing the exit hose and starting the heat while the car is running...if the pump is running the coolant flows like a fire hose.

-Chandra

With engine off, and key off for that matter, disconnect the electrical connector and connect power from the battery with jumpers and a DC ammeter in series with the connection. When you connect you will hear and feel the pump running. You should not read more than 1.3 Amps on the ammeter. If you read more than 1.3 Amps, replace the pump whether it runs or not because it will damage your climate control unit.

Good luck,

Mine is noticable since I do not have any heat at idle and at times even when car is running now that I have disconnected the aux pump.

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joel

Prayers bring forth enlightenment.

Larry,

I have been reading your posts about installing a fuse/resistor to safeguard the CCU. Could you elaborate on this, and maybe it should be posted in the DIY section. Thanks.

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joel

Prayers bring forth enlightenment.

Bought a new aux pump (got a good deal, $100), it is amazing what that small pump can do.

The heat is on at idle. Contrary to what I have reading, I believe this part has something to do with the overall cabin air management, not just the heater part.

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joel

Prayers bring forth enlightenment.

How quiet is your new pump? Can you hear it at idle? Mine still works and is within the amp limits but I can hear it while in the drivers seat at idle. Just wondering if they are normaly that loud.

Jorg

Are you sure it is the aux pump that is being loud? Both my old and new pumps doesn't generate any audible noise. The only sign the pump is working is the vibration you feel by holding it in the palm of your hands.

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joel

Prayers bring forth enlightenment.

On my 560SL I can see the little shaft coupling turning between the pump and the motor. When this unit is not working I get no heat at idel here in CT.

John Roncallo

I few folks have reported in the past that you can get by just fine without the aux water pump. They removed the pump and coupled the hose ends. They reported no perceptible change in heat output.

Have not tried this myself, but might be worth a try. Can always go back to the electric pump if it does not perform.

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1986 300E 5-Speed 240k mi.