MerCruiser 305 CID (5.0L) Service Manual page 742

SERVICE MANUAL NUMBER 24
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-
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-
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 nylon string. Position thermostat on string so that
c. Place thermometer in container and position so that bottom of thermometer is even
Index
90-861327--1 OCTOBER 1999
a - Check For Light Leakage Around Perimeter Of Valve
it will be just below water level when suspended, then allow valve to close. Suspend
thermostat in water.
with bottom of thermostat. Do not allow thermometer to touch container.
a - Thermometer
b - Nylon String
c - Thermostat
a
a
b
c
SEAWATER COOLED MODELS
72717
72675
Page 6A-21