Mercury 305 CID, Service Manual, Page: 798 / 967

6B-24 - CLOSED COOLING MODELS 90-823225--1 1096
4. Check opening and closing temperature of ther-
mostat (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. Po-
sition thermostat on nylon string so that it will
be just below water level when suspended,
then allow valve to close. Suspend thermo-
stat in water.
72675
b
c
a
a - Thermometer
b - Nylon String
c - Thermostat
c. Place thermometer in container and position
so that bottom of thermometer is even with
bottom of thermostat. Do not allow thermom-
eter to touch container.
IMPORTANT: When performing instructions “d”
and “e,” water must be agitated thoroughly to ob-
tain accurate results.
d. Plug in tester and observe temperature at
which thermostat opens (thermostat drops off
thread). Thermostat must open at 138-145
°
F
(59-63
°
C). Thermostat must be completely
open at 170
°
F (77
°
C).
e. Unplug tester and allow water to cool to a
temperature 10
°
F (5
°
C) below specified tem-
perature on thermostat. Thermostat must be
completely closed at this temperature.
f. Replace a thermostat that fails to meet all of
the preceding tests.
Installation
! CAUTION
Do not operate engine without cooling water be-
ing supplied to the seawater pickup pump, or
pump impeller will be damaged.
1. Remove thermostat housing and gaskets. Dis-
card gaskets.
2. Clean gasket surfaces on thermostat cover, ther-
mostat housing and intake manifold.
3. Position lower gasket (with continuity rivets) on
intake manifold. Place thermostat housing on
gasket.
IMPORTANT: If gasket has continuity rivets, do
not coat with Quicksilver Perfect Seal, or audio
warning temperature switch may not work
properly.
4. Install thermostat as shown, into thermostat
housing.
Stainless Steel
Thermostat
71801 72674
a
b
Brass Thermostat
a - Install Thermostat With This End (Down) Toward
Thermostat Housing