Anatomy of w114/w115 water pump
by Patryk Rebisz

A water pump is a simple device that is spun by engine's power to move water coolant through the engine. In essence it's an impeller sitting on bearings with a "spinner" on one end and a place to attach pulley on the other.

When it goes wrong it can create a havoc. When bearings go, the shaft can start wobbling with fan hitting various engine parts and disintegrating in the process.