Mercury 305 CID, Service Manual, Page: 808 / 967

6B-34 - CLOSED COOLING MODELS 90-823225--1 1096
Checking Coolant for Alkalinity
! WARNING
Coolant section of Closed Cooling System is
equipped with a 16 psi (110 kPa) pressure cap (fill
cap). Before removing pressure cap (in next
step), first allow engine to cool down, as sudden
loss of pressure could cause hot coolant to boil
and discharge violently. After engine has cooled
down, turn pressure cap 1/4-turn to allow any
pressure to escape slowly, then push down and
turn cap all-the-way off.
Coolant in closed cooling section of cooling system
should be changed every two years and should be
checked for alkalinity at least once between change
intervals. To check coolant for alkalinity, proceed as
follows:
1. Obtain pink litmus paper from a local supplier
(drug store, pet shop, etc.).
2. Remove pressure cap from heat exchanger and
insert one end of pink litmus paper into coolant.
3. If pink litmus paper turns blue, coolant is alkaline
and need not be replaced.
4. If pink litmus paper remains pink, coolant is not al-
kaline and MUST BE REPLACED, as explained
under “Changing Fresh Water Coolant,” follow-
ing.
Changing Coolant
DRAINING INSTRUCTIONS
1. Remove coolant recovery bottle and pour out
coolant.
! WARNING
Coolant section of Closed Cooling System is
equipped with a 16 psi (110 kPa) pressure cap (fill
cap). Before removing pressure cap, first allow
engine to cool down, as sudden loss of pressure
could cause hot coolant to boil and discharge
violently. After engine has cooled down, turn
pressure cap 1/4-turn to allow any pressure to
escape slowly, then, push down and turn cap
all-the-way off.
2. Remove pressure cap from heat exchanger.
3. Remove drain plugs on each side of cylinder
block or fitting, as shown.
74073
a
a
b
Carbureted Engines, Starboard Side (Port Side
Similar)
a - Typical Drain Plug
b - Sealing Washer
! CAUTION
Avoid product damage. Do not disturb the Y-fit-
ting when removing the drain plug. There is an
ignition control “Knock Sensor” in the upper
hole of the fitting. This sensor must not be loos-
ened or removed. It is tightened to a critical spec-
ification at the factory.
a
EFI Engines Starboard Side
75081
b
EFI Engines Port Side
a - Drain Plug - from Y-fitting
b - Drain Plug - from Cylinder Block