Is there a vent in the filler neck (actuated when the cap is screwed on)? If so, press on it to release the trapped air for faster filling to the brim of the neck. VW diesels have it, I'd imagine Mercedes has something similar.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked