I just bought a 1982 240D with manual transmission, 220K miles and I have a few questions I’d like to ask.

First what turns on the electric fan on the radiator? So far I have had it come on when the temperature seemed to be at a normal range. I have not had it come on with the AC nor has it come on when the engine temp was a little warmer then normal. So I was wondering what and when does it get turned on.

Second the return fuel line from the filter assemble seems to have a bulge in it and the book has a picture of this and it also looks like it has a bulge. Is it normal for this hose to have a bulge?

Third what kind of fuel mileage should I get with this car?

Thanks,