Mercury 305 CID, Service Manual, Page: 810 / 967

6B-36 - CLOSED COOLING MODELS 90-823225--1 1096
! CAUTION
DO NOT operate engine without water flowing
thru seawater pickup pump, as pump impeller
may be damaged and subsequent overheating
damage to engine or stern drive unit may result.
•
Front of engine should be higher than rear to
purge trapped air out of the system during ini-
tial filling. This will minimize the possibility of
air being trapped in the closed cooling sec-
tion which can cause engine to overheat.
IMPORTANT: This closed cooling system flows
coolant at a high rate. Higher idle speeds in-
crease dispersion of trapped air into system
making it more difficult to purge trapped air. Op-
erate at idle during filling and air purging when
specified.
2. Start engine and run AT IDLE. Add coolant
solution to heat exchanger, as required, to
maintain coolant level at filler neck. After engine
has reached normal operating temperature (ther-
mostat is fully open), and coolant level remains
constant, fill heat exchanger until coolant level is
into filler neck and begins to flow into coolant
recovery bottle plastic tubing.
3. Remove cap from coolant recovery reservoir and
fill to “Full” mark with coolant solution. Reinstall
cap.
4. Lift recovery bottle and plastic tubing above heat
exchanger filler neck. Allow coolant to flow down
through tubing to purge air through filler neck
fitting.
5. Install pressure cap on heat exchanger.
6. With engine still running, check hose connec-
tions, fittings and gaskets for leaks. Also observe
engine temperature gauge to make sure that
engine operating temperature is normal. If gauge
indicates excessive temperature, stop engine
immediately and examine for cause.
! WARNING
Allow engine to cool down before removing pres-
sure cap. Sudden loss of pressure could cause
hot coolant to boil and discharge violently. After
engine has cooled down, turn cap 1/4-turn to al-
low any pressure to escape slowly, then, push
down and turn cap all-the-way off.
7. Recheck coolant level after first open-throttle
boat test and add coolant, if necessary.
8. Maintain coolant level in coolant recovery reser-
voir between “Add” and “Full” marks with engine
at normal operating temperature.
Coolant section of Closed Cooling System should be
kept filled year around with recommended coolant
solution. DO NOT drain coolant, fresh water section,
for storage, as this will promote rusting of internal sur-
faces. If engine will be exposed to freezing tempera-
tures, make sure that coolant section is filled with
ethylene glycol antifreeze and water solution, mixed
to manufacturer’s recommended proportion, to pro-
tect engine to lowest temperature to which it will be
exposed.