Testing - Mercury MerCruiser MCM 454 Mag MPI Service Manual

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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

90-861326--1 MARCH 1999

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stat for leakage by holding it up to a lighted background. Light leakage around the ther-

mostat 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-

Check For Light Leakage Around Perimeter Of Valve

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 nylon string. Position thermostat on string so that

it will be just below water level when suspended, then allow valve to close. Suspend

thermostat in water.

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.

Nylon String

SEAWATER COOLED MODELS

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