I was going to ask a similar question today, but my issue is much more
dramatic than the OP's.  1979 300TD as many of you may remember...

When the car is running, there's a constant stream of bubbles going into
the fuel prefilter.  The hose leading to it is pretty old and beat, and
I'll be replacing it soon, but if I'm going to get soaked in diesel fuel
I want to know what all to look at.  Is the system closed, insofar as if
I don't purge the air properly it'll keep circulating, or is a lame-o
purge after changing the filters going to work itself out over time and
the air should just "go away" all by itself?  I wouldn't think that in
my case the hand pump leaking could cause this effect since the hand
pump is on the other side of the prefilter.  Could my fuel pump be going
bad?  ...but it looks like the pump is the part that the hand pump is
connected to, sooo...  The air appears to be coming from the tank.

...I suppose I'll just go and swap out all of the fuel lines and then
see what I get.  I never looked at the prefilter while the engine was
running before the filter change, but I'm pretty certain there was a
smaller volume of air in it.

When I did the filter change, I pumped and pumped and pumped, but didn't
get the point that I was supposed to release the 'out' line from the
main fuel filter.  Could that fact be causing me these problems?  The
car runs fine, but it doesn't start up as quickly as it did before the
filter swap.  Before the swap it would always fire on the first or
second crank, now it takes two to four to start when the engine is cold.

Thanks for any advice.

-tom!

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