Testing Closed Cooling System; Testing Coolant For Alkalinity; Pressure Testing System - Mercury MerCruiser D2.8L D-Tronic Service Manual

CLOSED COOLING SYSTEM

Testing Closed Cooling System

Testing Coolant for Alkalinity

Allow engine to cool before removing pressure cap as sudden loss of pressure
could cause hot coolant to boil and discharge violently. After engine has cooled,
turn 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 (fresh water) section should be changed every two years.
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 litmus paper into
coolant.
a. If pink litmus paper turns blue, coolant is alkaline and need not be replaced.
b. If pink litmus paper remains pink, coolant is not alkaline and MUST BE

Pressure Testing System

Allow engine to cool before removing pressure cap. Sudden loss of pressure could
cause hot coolant to boil and discharge violently. After engine has cooled, turn cap
1/4 turn to allow any pressure to escape slowly, then push down and turn cap all the
way off.
If coolant section of closed cooled system is suspected of leaking or not holding sufficient
pressure, and no visible signs of leakage can be found, perform the following test:
1. Remove pressure cap from heat exchanger or reservoir.
2. Clean and inspect pressure cap to ensure that cap is maintaining proper pressure in
system. Refer to Testing Pressure Cap.
3. Clean and inspect fill neck:
a. Clean inside of filler neck to remove any deposits or debris.
b. Examine lower inside sealing surface for nicks or other damage. Surface must be
c. Check locking cams on sides of filler neck to ensure that they are not bent or
4. Adjust coolant level in fresh water section to 25 mm (1 in.) below filler neck.
Page 6B-12
REPLACED. Refer to Changing Coolant.
perfectly smooth to achieve a good seal between it and rubber seal on cap.
damaged. If locking cams are bent or damaged, pressure cap will not hold the proper
pressure.
WARNING
WARNING
SERVICE MANUAL NUMBER 22
90-860074--1 FEBRUARY 2002