Home' Afloat : AFLOAT April 2014 Contents Take monthly with water April 2014 43
It goes against accepted
wisdom regarding diesel
engine care, but it only takes
one filter failure to pump the
tanks dry and the bilge full.
If this suggestion is followed,
always place a notice on
the ignition panel loudly
warning that the fuel is
A more extraordinary case of filter failure happened to a friend
who bought a small diesel launch at a fair price only to discover
that his prize had a problem the previous owner conveniently
failed to mention and presumably could not fix.
Namely, the engine constantly cut out for no apparent reason
despite my friend checking every inch of the fuel system over
and over again. There was nothing visibly wrong so he focused
his attention on the primary fuel filter, which happened to be
new and one of the best types on the market. All seemed to be
perfectly okay so he took it to the local agent who declared it to
be in perfect condition.
More frustrated than ever, my friend did a number of bench-
tests with the filter and was shocked to find that it was reverse
feeding despite all relevant plumbing being correct as per
instructions. That’s when it hit him: the flow arrows cast into
the filter’s body were pointing the wrong way! He reversed the
flow and it worked perfectly.
He then contacted the main agent who, despite not believing
him, referred the matter to the manufacturer who confirmed his
finding. This led to the recall of a whole production line of filters
that were flowing in reverse, their arrows somehow being cast the
wrong way around. Exactly how this happened I cannot say, but
I saw the errant filter for myself and greatly admired my friend’s
tenacity in discovering the problem.
The reader is unlikely to experience filter mysteries of this
magnitude, but if filters are not in your maintenance regime, then
sudden engine failure is a distinct possibility. It may be past time
to check them and at the very least make sure the primary filter
is the coarsest, not the finest. h
• ADVANCED TECHNOLOGY
• SUPERIOR QUALITY
26/17 Bowden St, Alexandria Sydney 2015
(02) 9319 5222
NANNI DIESEL AUST
The reliability of diesel engines is all about their robust
construction and absence of electrical dependence,
however, dirty fuel remains their archenemy.
Without clean fuel, diesels are subject to total failure when
you least need it, their filters sometimes becoming clogged at
the most inopportune time. It is vital that all filters are correct
for the job and are changed at the first hint of trouble – a classic
symptom being the engine slowing down or adopting an irregular
beat for no apparent reason.
These are early warning signs that a total shutdown is
imminent, hopefully not at a crucial navigational moment such
as when crossing a bar. Shutdown can happen from insidious
accumulation in one or more filters or by the fitting of the wrong
filter in the wrong place.
To expand on that last statement, if primary and secondary
filters are fitted to your system, the primary filter (the one
between tank and secondary filters) must be coarser than the
secondary filter otherwise it will be the first to clog and starve
This leads to engine failure despite the fact that all filters
may have only recently been fitted. This scenario is common
and is often the last one considered when trouble-shooting a
And then there are those extraordinary cases of failure that
cannot be blamed on the filter, as a friend discovered one night
while fast asleep aboard his vessel.
All was perfectly normal when he hit the sack, but during the
night constant clicking noises like an army of crustaceans battling
it out on the seabed below awoke him. Reluctant to believe it
was a mechanical sound, he eventually thought of checking
the engine. There, he saw that the bilge was slowly filling with
diesel as the fuel pump cut
in and out, thus causing the
Why? What could have
possibly happened during
the night to start the pump
running and, having started,
how could it possibly pump
fuel into the bilge?
The problem was quickly
identified as a cracked water
sight-glass in the primary
filter. It had always been an
object of periodic inspection,
but for some unknown reason
on that particular night the
glass cracked for no logical
reason, thus causing the pump
slowly but surely into the bilge.
This incident is a good
argument in favour of turning
off the fuel before leaving a
vessel for extended periods.
Fuel filter porosities are usually
stated in microns – coarse being
the best choice for primary filters.
FILTERS by Alan Lucas
A primary filter should have a
water-fuel separator glass as well
as well as a filter coarser than
downstream secondaries. Too
fine a filter in the primary unit is
a promise of premature engine
Links Archive AFLOAT March 2014 AFLOAT May 2014 Navigation Previous Page Next Page