Thermostat; To Replace The Thermostat; Raw Water Cooling Circuit; Raw Water Pump - Universal M3-20A Operator's Manual

ENGINE COOLING CIRCUIT
THERMOSTAT
A thermostat, located ncar the manifold at the front of the
engine, controls the coolant temperature as it continuously
flows through the closed cooling circuit. When the engine is
first started the closed thermostat prevents coolant from flow-
ing (some coolant is by-passed through a hole in the thermo-
stat
to
prevent the exhaust manifold from overheating). As
the engine warms up the thermostat gradually opens. The
thermostat is accessible and can be checked, cleaned, or
replaced easily. Carry a spare thermostat and gasket.
THERMOSTAT
.
_._._._
..
_
..
GASKET
~I
THERMOSTAT~
i
THERMOSTAT
HOUSING
To Replace the Thermostat
SEAL
Remove the two cap .screws and disassemble as illustrated.
When assembling the new thermostat and gasket put a thin
coat of sealant on both sides of the gasket before pressing in
place.
Run the engine and check for normal temperatures and that
there are no leaks at the thermostat housing.
14
RAW WATER COOLING CIRCUIT
The raw water flow is created by a positive displacement
impeller pump. This pump draws water directly from the
ocean, lake, or river from a through-hull opening through a
hose to the water strainer. The raw water passes from the
strainer through the pump to a heat exchanger (through the
heat exchanger tubes) where it cools the engine's circulating
fresh water coolant. The raw water is then discharged into the
water injected exhaust elbow, mixing with, and cooling the
exhaust gasses. This mixture of exhaust gas and
raw
water is
driven through the stern tuhe and overboard.
Raw Water Pump
TIle raw water pump is a self-priming, rotary pump with a
non-ferrous housing and a neoprene impeller. The impeller
has flexible vanes which wipe against a curved cam plate
within the impeller housing, producing the pumping action.
On no account should this pump be run dry as water acts as a
lubricam for the impeller. There should always be a spare
impeller and impeller cover gasket aboard (an impeller kit).
Raw water pump impeller failures occur when lubricant (raw
water) is not present during engine operation. Such failures
are not warrantable, and operators are cautioned to make sure
raw water flow is present at start-up.
RAW WATER PUMP
WEAR PLATE
HOUSING