CLOSED COOLED (FRESH WATER) MODELS
SERVICE MANUAL NUMBER 23
90-861326--1 MARCH 1999 Page 6B-11
Testing
1. Clean thermostat in soap and water to remove any deposits or debris.
2. Inspect thermostat for corrosion or other visible damage.
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3. If thermostat is suspected of producing insufficient engine temperature, check thermo-
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.)
4. Check opening and closing temperature of thermostat (using a tester similar to the one
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.
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a
b
c
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.
IMPORTANT: When performing instructions “d” and “e,” water must be agitated thor-
oughly to obtain accurate results.
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.
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