What is it?
 

I have a 1986 560 SEL. On the engine directly under the alternator there is some type of pump. It is driven by one of the belts and has two hoses attached. It has the words "no oiling" printed on the side. I checked under the hood and found that one of the hoses had become disconnected from the unit but the engine seemed to running OK anyway. I have re-attached the hose. Just what is this unit and what does it do?

I'm pretty sure that is the air pump but I'm not looking at a pic or anything...

Alan

air pollution pump
 

I believe you are talking about your air polution pump.

Sounds like the air pump. It comes on during initial cold start and pumps additional air into the exhaust manifold. If I remember correctly it is supposed to reduce NOx until the engine gets up to operating temperature. You can start the car and watch the pulley on the front of the air pump. The electric clutch should drop it out after the engine gets up to tempature.

Not sure about your particular model but if it is inoperative it can make the check engine light come on on some models.