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Discussion Starter #1
2000 ML320

There is what sounds like a motor thats constantly running near the battery connected to the coolant canister. Its very hot to the touch (the hoses) so im assuming it has coolant going through it, maybe for the heater? Its not my car so i dont know a lot about Mercedes and haven't invested in any tech books with diagrams.

Can anyone help me on this?
 

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2002 ML 320, 2004 Audi Avant A4
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Is this in the drivers side near the front of the engine bay?
 

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No its on the passenger side to the right of the battery, it says bosche on it and has 2 hoses connected through it and one electrical connector on the bottom of it.

The hoses are very hot so im assuming this thing has coolant running through it.
 

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1999 ML 430
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675 Posts
noreason said:
2000 ML320

There is what sounds like a motor thats constantly running near the battery connected to the coolant canister. Its very hot to the touch (the hoses) so im assuming it has coolant going through it, maybe for the heater? Its not my car so i dont know a lot about Mercedes and haven't invested in any tech books with diagrams.

Can anyone help me on this?
It's the auxilary water pump. i just replaced one..$112 at Duvals. Mine was real loud and the speed varied a lot.
 

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yeah i was thinking some kind of water pump. odd, ive never seen a car with an aux water pump. more crap to go wrong i guess. I'll let the owner know.

The part is very loud so I assume its going out? Does it NEED to be replaced?
 

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1999 ML 430
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noreason said:
yeah i was thinking some kind of water pump. odd, ive never seen a car with an aux water pump. more crap to go wrong i guess. I'll let the owner know.

The part is very loud so I assume its going out? Does it NEED to be replaced?
I think it keeps the cooling fluid circulating after the engine is turned off..my guess.. I just ordered one because I dont think you can repair it...
and I'm not going to risk my engine saving 100 bucks.... you right...I never had so much stuff break on any other car, including other MB's....strange...
 

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ML550, W212 E350 4 matic, 1966 Corvette C2 convt.
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It is a recirc pump thats there to evenly cool the engine after shut down. This prevents warping of the many aluminum engine parts. It should shut off after a few minutes or so.
 

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1999 ML 430
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I just changed the pump. Time is around 15 minutes. I also changed the rubber grommet because the old one is almost impossible to remove and for around 7 bucks you get a new one. Make sure that you align the new rubber grommet exactly like the old one and then try to slide it on to the new pump. The new rubber grommet is impossible to turn if you slide it on the new pump and it was very difficult to slide it on the new pump. Make sure you have rags all around because coolant will run all over the place. If I had to do it again I would get two rubber plugs the size of the hoses.
The new pump runs very quit and I think that most of the noisy pumps will fail soon.
 
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