My 2003 E320 (or W211 chassis w/ the M112.949 motor) has a healthy 208,000 miles on her now, and is still running like a champ.

For some time, I would hear an awful noise intermittently (particularly at idle) that sounded like a squealing/squelching noise that was very apparent.

To make a long story short, I came to the conclusion after some investigation (thought it was coming from the SBC or the ESP/ABS control module), I realized it was from that little black pump just below and in front of the unit (when looking at engine from front of vehicle, it's between and BELOW the passenger/left-side headlamp housing and the SBC control unit.

Moving right along... the pump is in total failure mode and doesn't operate at all anymore and leaks some. I have purchased the new pump (sorry Pelican Parts, but Parts.com had it for $330... and was about $100 more here ) and am awaiting it's delivery.

I understand I need to undo the hoses and detach the unit from the wiring harness and probably refill the coolant with MB compatible fluid)....
but are there any details I need to know about??

Thanks for any help! I really couldn't find ANY information on this service and the replacement part! I have learned it's function, but any more detail, etc would be greatly appreciated! I do know that I have no heat since it failed entirely (ie the squeezing stopped and started leaking slightly from the unit).

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2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

From what you've described (and thank you for all of the details, too many such posts are far too sketchy), it indeed needs to be replaced. It's just plug and play, but as you allude to coolant, when is the last time it was flushed and refilled with the proper mix of spec coolant and distilled water? If you don't remember, then this is as good a time as any. If you flush with tap water you should pull the block drains as well, but given the cost of distilled water at discount places (target, wallyworld) that's not a bad option either.

Good luck.

Plug and play? Great! That's what I was picturing.... but you just never know with these babies we have (our Benz's).

As for the coolant, yes, I replaced many components (hoses and expansion tank) about 10k miles ago... HOWEVER.... it seems as though the cooling system doesn't have much pressure? I don't know how much of this is attributed to the aux water pump failure, but probably plays a role.
Additionally, now with the pump failure, it's slowly leaking at aux pump also... and another place by the expansion take....

I'm just kind of curious what other reasons or components that are failing to lose pressure (A/C hasn't worked in 1 1/2 years, but compressor still activates, possible condensor failure??) if related.

ANd what about vacuum leaks? Never really understood the whole vacuum thing entirely.... but I know there have to be some by now.

So to answer your question, I've been filling it with tap water (or gas station water fill) often. I did do one 50/50 mixture of coolant but that obviously leaked out too.

I'm glad that you found my post concise! I used to post on this site all the time when I had my first benz... I miss it! It was Mercedesshop.com in those days. I think that maybe some of the reason that I stopped posting had to do with the large database of info that was gathered over time, thus not necessitating a new thread? I dunno!

PEACE!

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

Man it's been a looong time since you've last posted.

Don't be a stranger.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

I know, it's been forever!

I promise, I'm going to be much more active these days! I guess just out of the "groove."

How you been, Suginami?

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

ANd I've noticed that you've quadrupled my number of postings! I used to be top poster number 4 or something like that!

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

Doing well. Like I always say: I'm still here.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Due these aux water pumps only fail at very high mileage?

I wonder why there is so little info on the issue.

Do-dee-doo

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

More, so can anyone help me with regards to the lack of pressure in the coolant system - causes possible causes?

Additionally, is the aux water pumps only function to keep water moving when engine is off (and for REST feature) to avoid hot spots? It operates sometimes (or all the time?) when car is off? ANything else as to it's reason for being?

Thanks!

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

Also note that there are some cheaper alternatives. 1 is to replace the motor brushes, and the 2nd is to use a VW pump ( or just its motor), which runs around $100.

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Prost!