Fuel pump?
 

I have a 1983 Mercedes diesel. It has just started making a funny noise when I turn the key on but before I actually start the engine. It seems to be coming from the middle of the car, kind of just behind the driver's seat. Some people have told it's the fuel pump, while others have told me it's an extra fuel pump. They have also said that it could run for another year before the pump actually quits. What IS making his noise?

Any idea if it's been converted to run on veggie oil?

The 83 MB diesels all come stock with engine driven mechanical fuel pumps... So if you have an electric one, it's not stock.

No, it's not been converted. It runs on strictly diesel.

Put the car on ramps or jack stands and then turn the key on, climb under the car and look for what's making the noise. When you find it, take a picture and post here so we can see what it might be and give you advice and counsel accordingly.

If it's not coming from under the car, then start looking behind the seat until you find it. Again, take pictures and post.

I like the fact that your friends have come to the conclusion that the "pump" will run for another year without knowing if there even is a pump existing where the noise is coming from.

I personally think it's the muffler centering servo that is sticking. :)

Another prudent option would be to open the trunk and stick your head in it next time you turn the key.

There are two motors (if you have a sunroof) on the driver's side. antenna and sunroof.

Could it be one of the motors in your seats or head rest?

Did any W123's come with power seats? Mine didn't.

Never seen that either.

He has yet to identify the actual model car, so it could be a 126, 123 or even a c111!

Maybe even a bus...