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).