Mercury 305 CID, Service Manual, Page: 802 / 967

6B-28 - CLOSED COOLING MODELS 90-823225--1 1096
1. Remove seawater drain plug from bottom of heat
exchanger and allow water to drain. After water
has drained completely, coat threads of drain
plug with Quicksilver Perfect Seal and reinstall.
72718
b
c
d
a
e
a - Bolt
b - End Cap
c - Sealing Washer
d - Gasket
e - Drain Plug
2. Remove bolts which secure end plates to each
end of heat exchanger, then remove end plates,
seal washers and gaskets. Discard seal washers
and gaskets. Clean gasket material from end
plates and heat exchanger.
3. Clean water passages in heat exchanger by in-
serting a suitable size wire brush into each pas-
sage. Use compressed air to blow loose particles
out of water passages.
4. Apply Quicksilver Perfect Seal to both sides of
new end plate gaskets, then reinstall end plates,
using new gaskets and seal washers. (Be sure to
install seal washers between end plates and gas-
kets.) Torque end plate bolts to specifications.
! CAUTION
Avoid seawater pickup pump impeller damage.
DO NOT operate engine without water being
supplied to seawater pickup pump.
5. With boat in the water and/or cooling water prop-
erly supplied to seawater pickup pump, start en-
gine and inspect for leaks.
Flushing Seawater Section
of Closed Cooling System
If engine is operated in salty, polluted or mineral-
laden waters, seawater section of closed cooling
system should be flushed periodically (preferably
after each use) with fresh water to reduce corrosion
and prevent the accumulation of deposits in the
system. Seawater section also should be thoroughly
flushed prior to storage.
! WARNING
When flushing cooling system with boat out of
the water, be certain that area in vicinity of pro-
peller is clear and that no person is standing
nearby. As a precautionary measure, it is recom-
mended that propeller be removed.
! CAUTION
Do not run engine above 1500 RPM when flush-
ing. Suction created by seawater pickup pump
may collapse flushing hose, causing engine to
overheat.
! CAUTION
If cooling system is to be flushed with boat in the
water, seacock (if so equipped) must be closed,
or water inlet hose must be disconnected and
plugged to prevent water from flowing into boat.
! CAUTION
To prevent engine or stern drive unit damage
DO NOT run engine or drive unit without water
being supplied to water intake openings on gear
housing.
! CAUTION
Watch temperature gauge at dash to ensure the
engine does not overheat.
1. Follow instructions appropriate to your model:
NOTE: If flushing cooling system with boat in water,
raise drive unit to trailer position, install flushing at-
tachment and lower drive unit to full IN/DOWN posi-
tion.