MJM Yachts LLC 40z, Owner'S Manual

Page: 45 / 64

Chapter 9 Finishes, Equipment, and Appliances MJM 40z Owner’s Guide page 37
then sends it to the filters and injectors, where the
injector pump sends fuel to the individual cylinders
for combustion. Whenever you open the fuel line
between the tank and the engine (for example, to
change a filter element) air enters the line. Air may
also be sucked into the fuel line through cracked
seals and gaskets, poorly fitted connectors and
clamps, via the pick-up tube in the fuel tank, etc.
This air must be removed, because even a tiny air
bubble in the fuel line will block the flow of fuel, and
without fuel, the engine won’t start; if running, air in
the fuel line will cause it to stop. To clear your fuel
line of air, you must vent or “bleed” it out. Consult
your engine’s manual to identify the bleeding nuts;
paint them with white nail polish so you can easily
find them again, in the dark, at sea. Given decent
access to the engine, bleeding or venting air is a
simple procedure that everyone should be able to
perform. Using the engine manual, teach yourself
how to do this.
Be diligent about checking your lube oil and oil
filter
Diesel engines are rough on oil and usually
require more frequent oil and oil filter changes than
comparable gasoline engines. Follow the engine
manual’s recommendation for service intervals.
Carry spares on board. Between oil changes, use
the dipstick to check the oil level. Top it off as
necessary from your on-board lube oil inventory,
but don’t exceed the “full” mark on the dipstick;
more isn’t better. If you get erratic RPM readings or
can’t reach high RPMs, most likely you need to
replace one or both Racor fuel filters.
Minimize risk of fire
Diesel engines vibrate a lot,
and the typical marine diesel has a lot of wiring and
hoses attached to it, crossing it, behind it and near
it. Over time, as the engine vibrates, the fasteners
may loosen and fail, the wiring and hoses droop or
fall. One hates to see a loose hose or wire (such
as the primary wiring harness, or the power supply
to your fuel pump, or a hose to the hydraulic
pump) cross and contact a hot exhaust manifold,
for example; this could be a prescription for fire
due to abrasion of insulation around wire, or
chafing through the wall of a hose. From time to
time, inspect your engine compartment for these
potential risks. Add chafing protection, replace
worn insulation, and supplement the fasteners if
necessary. Consider rerouting wires and hoses
where appropriate
Know how to trouble-shoot the cooling system
Since overheating is a common problem,
familiarize yourself with engine’s cooling systems:
the raw water (sea-water) system, as well as the
fresh water (internal circulating coolant) system.
The most likely causes of overheating are:
• Raw-water valve closed.
• Raw-water through-hull blocked externally.
Check for a plastic bag, or a clump of sea
grass or other material, covering or plugging
the inlet.
• Cover of Raw Water Strainer improperly
secured allowing air in
.
•
Momentary air pocket preventing ingest of air
under boat. Reverse engine or stop and
restart.
•
Raw-water filter / strainer clogged with
sediment, sand, goo, grass, or living critters
such as barnacles, jellyfish, and algae.
•
Defective or destroyed impeller in raw water
pump. The impeller should be replaced every
year or two, as the rubber vanes become
brittle with age and may snap off.
•
Heat exchanger dirty or clogged up with
sediment and other deposits. The entire raw
water cooling system should be flushed
periodically to remove salt and sediment
deposits.
•
Exhaust elbow restricted by carbon deposits or
other solids, reducing discharge of cooling
water and exhaust gases. Routinely run the
boat at high RPM for several minutes to clear.
•
Thermostat stuck closed; likely will require
removal or replacement. (Note: Some diesel
engines operate OK - temporarily - without a
thermostat.) Coolant temperature of 170-180
o
F is normal.
• Low level of coolant (50-50 mix of antifreeze-
water). Coolant levels should be checked
routinely at the expansion tank, adding more as
needed. Don’t overfill (coolant). Alarm usually
sounds if coolant level is too low.
• Broken or slipping V-belt, which drives the
water pumps and the alternator. Even a new
belt deserves re-tensioning and inspection.
Suspect slippage or wear if you see dark “belt
dust” settling at the engine’s base. Belt tension
is OK if pressure deflects the belt by about 1/2
inch.
•
Overloading of the engine: Rope wrapped
around propeller shaft, dirty bottom, fouled
propeller, or air leaks in the raw water-cooling