Testing - Mercury MerCruiser MCM 454 Mag MPI Service Manual

SERVICE MANUAL NUMBER 23

Testing

1. Clean thermostat in soap and water to remove any deposits or debris.
2. Inspect thermostat for corrosion or other visible damage.
3. If thermostat is suspected of producing insufficient engine temperature, check thermo-
4. Check opening and closing temperature of thermostat (using a tester similar to the one
IMPORTANT: When performing instructions "d" and "e," water must be agitated thor-
oughly to obtain accurate results.
Index
90-861326--1 MARCH 1999
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stat for leakage by holding it up to lighted background. Light leakage around the thermo-
stat valve indicates that thermostat is not closing completely and should be replaced.
(A small amount of leakage at one or two points around the valve perimeter is accept-
able.)
shown), as follows:
a. Fill tester to within 1 in. (25 mm) of top with tap water. Do not use distilled water.
b. Open thermostat valve and insert thread. Position thermostat on nylon string so that
it will be just below water level when suspended, then allow valve to close. Suspend
thermostat in water.
a
a - Thermometer
b - Nylon String
c - Thermostat (Typical)
c. Place thermometer in container and position so that bottom of thermometer is even
with bottom of thermostat. Do not allow thermometer to touch container.
d. Plug in tester and observe temperature at which thermostat opens (thermostat
drops off thread).
e. Unplug tester and allow water to cool to a temperature 10 F (5 C) below specified
temperature on thermostat. Thermostat must be completely closed at this tempera-
ture.
f. Replace a thermostat that fails to meet all of the preceding tests.
b
c
CLOSED COOLED (FRESH WATER) MODELS
75747
72675
Page 6B-11