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IMPORTANT
Removal of the pressure cap when
the engine is hot can cause severe
injury from scalding hot water under
pressure. Always allow the engine to
cool and then use a large cloth when
turning the cap anti-clockwise to the
stop. This allows the pressure to be
released. Press firmly down on the
cap and continue to turn
anticlockwise to release the cap.
YACHTS AND LAUNCHES WITH HEAT EXCHANGER COOLING
It is essential that a 33% to 50%
anti-freeze/water mixture is used.
This not only stops freezing up in
winter, but it prevents overheating
and corrosion.
The warranty is invalid unless the
correct ratio is used.
SEA WATER PUMP AND COOLING SYSTEM
(HEAT EXCHANGER-COOLED
ENGINES)
CAUTION
Before working on the sea water
system ensure that the sea cock is in
the off position.
(1) It is very important that the
correct sea water flow is
maintained to cool the closed
circuit system of the engine. The
key component in this system is
the sea water pump impeller.
This should be checked every
year by removing the circular
plate (see fig. 2h).
(2) Withdraw the rubber impeller
from its drive shaft as shown.
See diagram 2i.
(i) Repeat (h) if coolant level is more
than one inch below the base of
the filler neck when the engine
has cooled down.
(j) Run engine on
2
/
full load for 20
3
minutes, check for leaks and
repeat (i).
(k) Anti-freeze solutions should be
drained off every 2 years and
replaced with a new solution.
Concentration of ethylene should not
exceed 50%.
The anti-freeze in the fresh water
system enables the boiling point of
water to rise to 124°C with a 13 psi
pressure cap fitted. The water
(3) Check impeller for cracks in the
rubber, excessive wear or lost
vanes. Replace with a new
impeller as necessary.
Note: If any pieces of rubber
impeller are missing then they
must be found as they are most
likely to be trapped in the
entrance to the heat exchanger
cooling stack. See 'Cleaning Tube
Stack'.
11
Note: When draining fresh water
system, ensure the engine has cooled
sufficiently to prevent scalding from
hot pressurised water. Prior to
draining a cold engine, remove the
filler cap from the header tank and
then open the water drain tap. This
allows the water to drain freely from
the system.
temperature alarm switch will
however be activated at 95° to
100°C. If no anti-freeze or a very
weak solution is used, then the water
temperature switch may not be
activated before coolant is lost.
Fig. 2h
Fig. 2I
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