and saves the filters. More than half a cup of water in
the bottom of the tank indicates a problem that should
be investigated. For example, the fuel vent may be
allowing water to flow back into the tank.
- Use a water filter
Use a water-separating primary fuel filter. The primary
filter, located off the engine between the tank and fuel
pump, should have a water-separating element and a
drain cock. The filter element should be 10 microns, and
two microns on the secondary filter. Tests have shown
that using two-micron elements in both filters clogs the
primary filter too soon and is not as effective as the
combination of 10- and two-micron filter elements.
The interval between filter changes depends on
a number of factors, including the amount of fuel
filtered, condition of fuel and the time interval. If no
vacuum gauge is fitted the primary should be changed
a minimum of once a year. A vacuum gauge measures
the amount of ‘suck’ (i.e. blockage).
Human eyes can only see down to about 30 microns,
so it shouldn’t be assumed that a filter element doesn’t
need to be replaced just because it looks clean. This
can be a dangerous and expensive mistake, potentially
causing engine failure at a critical moment such as
entering a harbour in adverse conditions.
The filter unit should be sized to handleat leastthe
total flow of fuel (i.e. fuel used + fuel returned to
tank). The larger the filter element, the less likely it is
to get blocked when any sludge in the bottom of the
tank gets churned up in choppy conditions. Always
keep two or three spares on board, even more if going
to remote areas. Small filter elements can get plugged
alarmingly quickly in rough conditions. - Secondary fuel filter
The secondary filter, located on the engine just before
the injection pump, is your last defence against
contamination getting into the injection pump and/
or the injectors. This can cause rough running, the
engine to stop or other serious and expensive damage.
The filter element may be a spin-on canister (like an
oil filter) or a disposable element inside a screw-on
metal cup, like most primary filters. Unfortunately, many
canister-type filters from engine manufacturers fail to
state the micron size, and often it is larger than two
microns, the recommended size for the secondary filter.
Change the secondary filter on each second change
of the primary filter (e.g. every second year) or
more often if the primary filter needs to be changed
frequently. Filters are inexpensive protection, so it is
better to change them sooner rather than later. - Bleed the diesel system
Air must be bled from the fuel system any time work
has been done on it because the engine will not run
with air in the fuel line. While some engines today are
designed to be self-purging (self-bleeding), this may
not always work, so it’s important to know how to
complete this task manually.
Always clean up any spilled diesel as it can cause
wiring and hose materials to degrade.
Best practice is to manually bleed air from the
system by loosening the bleed screw on the top of
the secondary fuel filter; one half-turn should be
enough. Following this, pump the lever on the lift/
transfer pump until only fuel and no air comes from
the bleeder. Fuel or air can be felt moving through the
pump and the air feels ‘spongy’.
If a mechanical lift/transfer pump is jammed or
‘locked up’, the engine will need to be rotated
manually using a large spanner or socket on the
crankshaft nut on the front of the engine. Most
engines rotate clockwise at the flywheel (right-hand
rotation), so should be turned anti-clockwise at the
timing belt. However, this is not the case for all, so
remember to check the manual first to ensure you’re
rotating in the right direction.
An electric fuel pump is activated by turning the key
but not cranking the engine. The pump will run until
pressure builds up and then switch off automatically.
Precautions must be taken if attempting to bleed air
by cranking the engine. Use the stop solenoid or stop
cable to prevent the engine starting and do not crank
the starter for more than 10 seconds before allowing
it to cool.
If the vessel is in the water, raw water will flow into
the exhaust water-lift muffler when the engine is
cranked and is not expelled by exhaust gases. Water
from the muffler can back up and flood the engine.
This is known as hydro-lock.
It’s also important to drain the water-lift muffler
or disconnect the raw water hose from the exhaust
outlet, allowing the water to drain into the bilge
when the engine is cranked, but ensure the hose is
reconnected before running the engine. If the boat is
out of the water, remove the raw water impeller as the
impeller vanes will be damaged if run dry.
Air will also need to be bled from the injection pump
and injectors if the engine has run out of fuel, or if
work was done on the injection pump, fuel lines or
injectors. This is a straightforward procedure, but
check in the engine manual for the specific location
of bleed screws and further instructions. Always use
two spanners when loosening or tightening injector
pipes to avoid twisting and kinking a pipe as this may
create a pinhole.- Injection pump and injectors
Although injection pumps require minimal maintenance,
they should not be neglected or tinkered with.
Any adjustments should be made by a professional
injection pump shop. Keep the area around the pump,
pipes and injectors clean. Also check for any signs of a
Above:If the
mechanical lift/
transfer pump is
jammed or ‘locked
up’, the engine will
need to be rotated
manually using
a large spanner
or socket on the
crankshaft nut on the
front of the engine.“The
secondary
filter is your
last defence
against
contamination.”
“It’s a good
idea to avoid
buying diesel
within three
hoursofa
fuel delivery.”
bluewatermag.com.au 53A reliable diesel supply