My 1997 300D has difficulty starting when the tank is half a tank full or
less. Is there a problem with the fuel pump or pickup? It doesn't matter
what the temperature is outside for this to happen. It starts just fine when
the tank has more than half full.
A possibility is that the fuel prefilter is partly clogged and
restricting the flow of fuel.
I have the same symptom on my 1977 300D when my prefilter is getting
clogged. The underlying cause is so-called "algae" living in the fuel
and breaking it down into a black sludge. That would likely be the
problem where you must change the filter frequently (i.e.,
significantly more often than the 30,000 miles recommended by MB).
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