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Old 04-20-2004, 04:41 AM
Registered User
Join Date: Apr 2002
Posts: 263
Bad auxiliary water pump?

Hey all:
What are the symptoms of a bad auxiliary water pump? My car's heater is always on due to a bad climate control. However, the heat increases from the defroster when I increase my car's speed. Is this a bad auxiliary water pump or heater valve? Thanks.

1985 190E 2.3-16 Euro
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Old 04-20-2004, 08:19 AM
Join Date: Jan 2003
Location: Florida
Posts: 1,084
Aux pump

The pump only runs when you hit the "rest button" it uses the residual heat in the cooling system to provide heat with the engine off. In some cars it also circulated the coolant if the engine was turned off but very hot. I dont think yours was one of them
The default for the "mono" valve is open, that means it needs voltage to shut off, so coolant is flowing if you have a defective heater module that does not provide voltage for the closure. The logic would be, the faster you go the more air thru the system, the more heat. You could bypass the valve for a period of time
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Old 04-20-2004, 09:26 AM
Registered User
Join Date: May 2003
Location: DC Metro Area
Posts: 365
Rest function

Does anyone know if the rest function was offered on W124 E-class cars? I'd love to be able to circulate my coolant after I turn off the engine. In summer, that sucker can get pretty hot.

1995 E420 79k
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Old 04-20-2004, 09:57 AM
Registered User
Join Date: Oct 2003
Location: New Mexico
Posts: 29
Years ago, I had an aux water pump start leaking on a 190. Since I was in the middle of a ski trip and it was Christmas eve (no dealer within miles), I bypassed the water around it and drove without it. After I returned home a few days later, the pump was replaced under warranty. I could never tell any difference in the heating system, before or after. I guess it must do something but in the normal heater operation, it must not do much.

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