COOLING
90-883728 JULY 2001 Page 4B-9
Troubleshooting
Thermostat Test
1. Inspect thermostat covers and cylinder head covers (thermostat opening) for cracks and
corrosion damage that could cause leakage. Replace parts as necessary.
2. Remove and discard gasket from each thermostat.
3. Wash thermostats with clean water.
4. Using a thermostat tester, similar to the one shown, test each thermostat as follows:
a. Open thermostat valve, then insert a thread between valve and thermostat body. Al-
low valve to close against thread.
b. Suspend thermostat (from thread) and thermometer inside tester so that neither
touches the container. Bottom of thermometer must be even with bottom of thermo-
stat to obtain correct temperature of thermostat opening.
c. Fill thermostat tester with water to cover thermostat.
d. Plug tester into electrical outlet.
e. Observe temperature at which thermostat begins to open. (Thermostat will drop off
thread, that was installed in Step “a”, when it starts to open.) Thermostat must begin
to open when temperature reaches 140 °-145 °F (60 °-63 °C).
f. Continue to heat water until thermostat is completely open.
g. Unplug thermostat tester.
h. Replace thermostat, if it fails to open at the specified temperature, or if it does not
fully open.
NOTE: BE SURE that water in thermostat tester is allowed to cool sufficiently [below 110
°
F
(43.3
°
C)] before testing the other thermostat.
51087
IMPORTANT: DO NOT operate engine without thermostats installed.
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