On Sun, 12 Aug 2007 08:20:15 -0400, "Roger Long"
wrote:

In 38 years around boats with auxilliary engines, I've never actually
experienced a clogged fuel filter

Count your blessings. You've either been lucky or been only on
exceptionally well maintained boats.

so I'm curious what the first signs are,
at least for slow build up as opposed to the fuel line suddenly sucking up a
mess that's been kicking around in the bottom of the tank.


You don't always get much warning with a clogged filter. Sometimes
the engine will begin to run a bit rougher and/or skip a beat now and
then. Those are serious symptoms on a diesel and should be
investigated immediately. More often, especially with a small engine,
your first warning will be a momentary speed up followed by a shut
down. That's when you get to practice changing filters at sea and
bleeding the injectors while you are upside down in the engine
compartment. It is also a good test for sea sickness issues and your
ability to remove foul smells from the bilge.

I would expect that slowly developing problems would first show up at
maximum RPM and fuel flow and that the engine would continue to run properly
for a time at lower power. If I make it a practice to bring my engine up to
full RPM at least once during every run, I should first see a failure to
reach the usual number, perhaps accompanied by some smoke due to the
injectors not getting enough fuel for the rack setting. Backing off to my
usual cruising fuel flow, which is about 60% of WOT, should give me plenty
of running time to get to a place where I can safely change the filter.

Next year, I'll put in a vacuum gauge but, in the meantime, will this
strategy work?

Not necessarily but it can't hurt. Without a vacuum guage your best
defense is to frequently monitor the sediment bowl on your Racor by
draining off a bit at the end of the day into a clear container. Shine
a light behind it and look for sediment particles and a water
separation layer at the bottom. If you are not getting much gunk in
the sediment bowl your tanks are clean and the filter should last
quite a while, probably a full season. If you are getting gunk in
the bowl you are at much higher risk and should first take steps to
get the tank cleaned up.

The risks are much higher in rough seas when the boat is rolling and
pitching. Extra vigilance is required in those circumstances because
the boat motion stirs up sediment in the bottom of the tank and a clog
can happen very quickly. I monitor my vacuum guages every hour in
conditions like that and I've seen a large filter go from almost no
back pressure to very high in that space of time. I've got large
tanks however and recirculate 40 to 50 gph.

The only time I've had serious issues with a small sailboat aux was
from failure to check the filter bowl after a long day's run. The
next day, back pressure in the Racor built up high enough to dislodge
the O-ring and much of the gunk ended up in the engine mounted
secondary which was not only a bear to change, but also difficult to
locate replacement filter elements. I spent the better part of a 2
week vacation at Marthas Vineyard locating replacement filters and
bleeding/rebleeding the injection system.