I've noticed that the in-line fuel filter on my 240D will have 4-5mm of fuel at the bottom or fuel injector side of the filter while the car is running and the fuel looks like it dribbles into the fuel filter. Acknowledging that the flow to the filter is a gravity feed I still don't think this is the flow of fuel that I'd expect. I've removed the filler cap and there was no change. My question is, is this normal or do I need to clean out or replace the tank filter?

Oh, and the in-line filter does fill once the car is tuned off.

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Fred Johnson
1977 240D
1983 300SD

Air in the inline filter is normal. If the filter wasn't transparent, you would never know it had air inside and you wouldn't worry about it. If any of the air should be pushed or sucked into the secondary (can type) filter, it will escape thru the air bleed hole and return to the fuel tank.

Technically, the fuel in the filter is not put there by gravity. It is pushed there by atmospheric pressure when the fuel pump applies a suction (pressure less than atmospheric pressure) to the pump side of the filter. I will admit though, that atmospheric pressure is created by gravity so in an around about way, the fuel is put into the inline filter by gravity.

P E H