"Grumps" wrote in message
...
squelchy wrote:

snip


OK. Our local garage (not BMW main dealer) has checked all possible issues
and has found nothing! Of course, the engine starts perfectly at the
moment.


One thing they noticed was that the fuel filter is new(ish), and wondered
if there was a fault with this or its fitting.

That's a possibility. I would check it out.

How exactly does a fuel filter work, and what would cause it to sometimes
stop the engine from starting?


The frequent enemy of a diesel engine fuel system is _air entering it_.
In the case of filters, there usually is a round detachable housing which is
sealed by a rubber ring. You should _always_ replace that ring (supplied
with the new filter element). Sometimes several different rings are
supplied, and you should compare the new one with the old one.
This rubber ring is not always easy to fit, and I always used a mirror to
make sure that it was seated properly. The assembly that the fuel element
housing fits to has usually an input connection and an output one. These
don't normally give problems, but _sometimes_ they do (they allow air to
come in). Cleaning these joints with petrol, drying carefully, and using
some jointing compound (red hermetite is ok) on all the threaded parts,
etc.. will usually work. I don't normally endorse using jointing compound,
unless a part is unobtainable or excessively costly.

Sylvain.

Sylvain.