What is this?

[LukeAnthony]

I know there are a lot of us out there that don't know everything about our car but would like to fit it without going to a shop. I would like to start a thread where we post a pic and the Mercedes Experts can help us identify and refer where we can get the parts. 

My part. This thing was connected by a hose to the Heater Servo.  I believe it's a valve but cannot find the part # or reference to it online. Any help would be appreciated. Here is a picture.

[daantjie]

Looks like aftermarket auxiliary water pump. Circulates water through the system at faster rate like when the engine is at idle.  Only replace with Bosch OEM. The MTC units are total garbage.

[13B]

Part of the Webasto extreme cold climate engine block warmer?

[Diesel 617]

Auxiliary Water Pump
# 0008356964

[daantjie]

Part of the Webasto extreme cold climate engine block warmer?

Nope nothing to do with the Webasto system.