Description; Maintaining Coolant Level - Mercury MerCruiser MCM 454 Mag MPI Service Manual

SERVICE MANUAL NUMBER 23

Description

There are several configurations of this cooling system, but the operation is essentially iden-
tical. Basically, the system is composed of two separate subsystems: the seawater system
and the closed cooling system. The seawater system is similar in function to the fan used
in an automobile because it absorbs heat (from the closed cooling system) as it passes
through the heat exchanger. The closed cooling system is similar in function to the rest of
the cooling system in an automobile.
The coolant recovery system keeps the reservoir full. Normal coolant overflow into recovery
bottle is approximately 1/2 pint (230 mL) during warm-up. The coolant recovery system
draws coolant back into the reservoir from the recovery bottle as the engine cools. As long
as there is coolant in the recovery bottle, the reservoir should remain completely full. If not,
there is a vacuum leak, usually at the hose leaving the reservoir, or the gasket under the
recovery filler cap. The gasket seals against the outer rim of the filler neck.
IMPORTANT: The coolant (antifreeze) flows around the outside of the cooling tubes
while seawater flows through the inside of the cooling tubes in the heat exchanger.

Maintaining Coolant Level

Before starting engine each day, ensure that coolant is visible in coolant recovery bottle.
If coolant is not visible, check fresh water section of cooling system (including coolant recov-
ery system) for leaks and repair, as necessary. Refill fresh water section with recommended
coolant solution, as outlined under "Changing Coolant," following.
If coolant is visible, start engine and run until it reaches normal operating temperature, then
recheck coolant level in coolant recovery bottle. Coolant level MUST BE between the ADD
and FULL marks (on front of bottle).
Allow engine to cool before removing pressure cap, as sudden loss of pressure
could cause hot coolant to boil and discharge violently. After engine has cooled,
turn cap 1/4 turn to allow any pressure to escape slowly, then push down and turn
cap all the way off.
If level is low, remove fill cap from coolant recovery bottle and add required amount of cool-
ant solution. Refer to SECTION 1B for coolant recommendations.
Index
90-861326--1 MARCH 1999
Downloaded from https://needmanual.com/
Coolant Recovery Bottle
a - Fill Cap
a
WARNING
CLOSED COOLED (FRESH WATER) MODELS
72520
Page 6B-3