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What is this unit in front of the SBC? When I turn the key, not necessarily starting the car it will make a humming, buzzing sort of noise. It continues after I shut the key off for a while.
The hose is 211 830 2515 which connects to a circulation pump. It appears to be an electric radiator supplemental pump to pump coolant around for a bit after shutting off the engine. It appears to pull from a connector off of the water pump and discharge to return lines that eventually make it back to the radiator.
Here is the EPC showing the water flow.
The pump is 300, see it pulls from the water pump. Then it pushes it via hose 250 to hose 100 or 110 depending on model. There it diverts it into and out of the washer reservoir and to the control value for the heater core where it will return back to the heater core return line.
My best guess is that this pump is the only way for engine coolant to heat the washer fluid, so maybe it runs all the time whenever the key is on. And the main cpu may have a timer in it, to keep it running for some period after turning off the key. I have never looked at this system on our e320. From the EPC all W211's have this unless you have option 228 (auxiliary heater).
I'm going to add this to the hoses to inspect next time I service our car. If the pump is making noise, it may be near end of life. Part number 211 835 02 64. FCPEuro has the bosh unit for under $60.
FCPEuro has this description:
The Auxiliary Water Pump has a primary function of circulating warm coolant to the heater core. If a small amount of coolant is circulated the blower fan will pull heat out of the coolant causing the heater core to get cold.
Interesting-thanks! I think I read something in the manual about a heater with the engine off function. It would make sense if it were connected to that too.
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