Engine Cooling Circuit; Description; To Refill With Coolan - Universal M3-20A Operator's Manual

ENGINE COOLING CIRCUIT
DESCRIPTION
The engine is fresh water cooled (engine coolant) by an
engine-mounted heat exchanger. Raw water is pumped
through the heat exchanger by a gear-driven, positive dis-
placement impeller pump. After the raw water cools the
engine coolant in the heat exchanger, it mixes with the
engine's exhaust gases, cools the exhaust gases, and dis-
charges overboard.
The engine's coolant is circulated by a belt-driven centrifu-
gal-type metal impeller pump mounted on the front of the
engine. The engine's coolant temperature is thermostatically
controlled.
The engine's coolant must be changed according to the main-
tenance schedule in this manuaL If the coolant is allowed to
become contaminated,
it
can lead to overheating problems.
ACAUTIDN:
Proper cooling system maintenance is
critical; a substantial number of engine failures can be
traced back to cooling system corrosion.
COOLANT
ORAIN
M
~;AIEN:SISFOiiiliEO
f' CAP
RECOVERY
TANK
MANIFOlO
A coolant recovery tank allows for engine coolant expansion
and contraction during engine operation, without any signifi-
cant loss of coolant and without introducing air into the cool-
ing system. This tank is best located at or above the engine
manifold level. and should be easily accessible.
13
Drain the engine coolant by loosening the drain plug on the
engine block and opening the manifold pressure cap. Flush
the system with fresh water, then start the refill process. See
the Parts Identification photos in this manual for locations.
NOTE:
The petcack on the heat exchanger can also be used fo
help drain engine coolant.
AWARNING:
Beware of the hot engine coolant. Wear
protective gloves.
To Refill With Coolant
With the engine running in idle, slowly pour clean premixed
coolant into the manifold.
NOTE:
Open the petcacks on the thermostat housing and heat
exchanger to heip remove air from the system. When a steady
flow of coolant appears at the drain plug opening, close the
water drain plug and continue to fill the system until the
manifold remains full. Close the petcock on the heat
exchanger when antifreeze flows from it.
Monitor the coolant in the manifold and add as needed. Fill
the manifold to the filler neck and install the pressure
cap.The petcock on the thennostat should also be opened
when refilling to allow trapped air to escape.
Remove the cap on the coolanl recovery tank, fill with
coolant mix to halfway between LOW and MAX, and
replace the cap. Run the engine, close all petcocks and
observe the coolant expansion tlow into the recovery tank.
After checking for leaks. stop the engine and allow it to cool.
Coolant should draw back into the cooling system as the
engine cools down. Add coolant to the recovery tank
if
needed. Clean up any spilled coolant.
NOTE:
Periodically check the condition of the pressure cap.
Ensure that the upper and lower rubber seals are in good
condition and check that the vacuum valve opens and closes
tightly. Carry a spare cap.