Westerbeke WPDS-20 Technical Manual page 63

R2
3. SEA WATER SYSTEM
The engine is indirectly cooled by the unrestricted fast-flowing stream
of sea water which absorbs the heat from the freshwater via the heat exchanger.
This raw water is picked up from the sea by a powerful neoprene impeller sea
water pump, and passes through the oil cooler to the heat exchanger. After
passing through the heat exchanger (and transmission oil cooler if installed),
the raw water is then piped overboard.
The oil cooler conducts heat away from the bearings and other friction
surfaces by the lubricating oil, which js circulated by the oil pressure pump
and cooled by the flow of sea water through the tubes of the oil r.ooler. When
the engine is equipped with a water cooled transmission for a hydraulic or RB
sailing gear the sea water is also circulated through the tubes of a transmission
oil cooler, and then piped overboard. In this sense both the engine oil cooier
and transmission oil cooler are heat exchangers.
4. SEA WATER PUMP
The water pump may be belt driven or mounted on t~e front of the timing
cover and driven from the fuel pump gear. The water pump is a selfpriming,
positive displacement rotary pump, with a brass case and a neoprene impeller.
The impeller has flexible vanes which wipe against a curved cam plate in the
impeller housin9, producing the pumping action.
NOTE: As the water pump contains a neoprene impeller, on no
account should it be run in a dry condition. Always
carry a spare impeller and gasket.
5. DRAIN COOLING SYSTEM
Remove the pressure cap from expansion tank and open the petcock on the
side of the cylinder block behind the starter motor, and the fresh water drain
petcock on the bottom of the heat exchanger. (Forward petcock) Turn petcocks
counter-clockwise to open.
6. FILLING COOLING SYSTEM
Ensure that the petcock on the side of the cylinder block and the petcock
on the bottom of the heat exchanger are closed. Turn clockwise to close. Remove
fill cap on top of expansion tank and pour cooland into system to one inch from
the top of the tank. Start engine and run
~ntil
normal operating temperature
is reached. Stop engine, carefully remove the cap and add coolant as required.
7. IMPELLER REPLACEMENT
a. Remove front end cover and gasket.
b. Remove impeller.
c. To replace the neoprene impeller coat the impeller and impeller chamber
with a good grade water pump grease only.
d. Align impeller key way with shaft key. Care should be taken that the
impeller blades all lie in the same direction relative to the rotation of
the pump, i.e., blades trailing.
e. Secure end cover and gasket with four screws and lockwashers.
f. In the event of wear being present en end cover, the cover may be reversed.
8. THERMOSTAT
a.
Drain cooling system (approximately two quarts).
b. Remove the nuts retaining the thermostat housing to the cylinder head
and lift up housing.
c. Lift out thermostat.