What Is This Extra Outlet On The Water Pump?
 

What is this extra outlet below the pulley? Is that the weep hole (or weep nozzle as it appears)?

On my old 400E, there was a brittle black plastic hose (approx. 3/8" OD) that is designated as a "tank with cooling line" (see #110 in picture). It tapped off a similar looking port on my water pump and ran vertically down to the front outside base of my oil pan. The tank attached with a screw. I think it was some sort of catch tank for the water pump. I installed a new pump, but never replaced the hose or tank and it never seemed to matter. Have you checked the EPC for your car to see if there is a similar part?

The OEM pump# for my car is 104 200 4701. This cross references to 104 200 4901, which is what I have.

In looking at photos the pumps all have this hole; I just never noticed it. Only a couple, mine and it appears Laso brand pumps also have the extended nozzle/hose fitting.

This one also has the mod kit to close off the rear outlet and one of the sensor ports on the top is sealed. I have two so I can use the open one on the side.

Weep hole.

mbdoc, have never seen a weep hole like that. Certainly looks like a hose connector to me. A weep hole is, as the name suggests, a small hole (approx. 1/4" diameter) in the bottom of the water pump casing that weeps coolant when the shaft seal is leaking. When the weep hole leaks coolant you know it's time to replace the water pump.

This one appears to have the connector to allow you to connect a hose to direct weeping coolant wherever you want.

Other new pumps have the hole; just not the connector (except for Laso-branded). I am guessing that the square reservoir on the structure that the water pump, tensioner and PS pump(?) bolt onto is a relatively recent addition for capturing leaking coolant, thus the elimination of the hose attachment.

Replaced my pump yesterday. The OE MB pump also has it.