Installation - MerCruiser GM4 Service Manual

4. Check opening and closing temperature of the
thermostat (using a tester similar to one shown
below), as follows
a. Fill tester to within 1 inch (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 sus-
pended, 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 ther-
mometer to touch container.
a
c
a - Thermometer
b - Nylon String
c - Thermostat
IMPORTANT: When performing step d thru f, wa-
ter must be thoroughly agitated to obtain accu-
rate results.
d. Plug in tester and observe temperature at
which thermostat opens (thermostat drops off
thread). Thermostat must open at specified
temperature stamped on thermostat.
Index
90-816462 2-695
b
72675
e. Continue heat water until a temperature 25 F
(14 C) above temperature specified on ther-
mostat valve must be completely open at this
temperature.
f. Replace a thermostat that fails to meet all of
the preceding tests.

Installation

1. Clean gasket surfaces on thermostat cover and
thermostat housing.
2. Place thermostat in thermostat housing with ther-
mostatic element end toward housing. Be sure to
position thermostat so that mounting flange fits
into recess in thermostat housing.
3. Coat both sides of new thermostat housing gas-
ket with Quicksilver Perfect Seal and position on
thermostat cover and torque bolts to 30 lb. ft. (41
N·m)
b
a
a - Thermostat Cover
b - Attaching Bolts
4. Reconnect hose to thermostat cover.
5. Start engine and inspect for leaks.
SEAWATER COOLED MODELS - 6A - 3
73572