5. Check the condition of the locking tabs on the cap. Replace the cap if the tabs are bent or cracked.
a - Locking tabs (one not shown)
b - Rubber seal
c - Gasket
6. Using a cooling system pressure tester, test the cap to ensure that it releases at the proper pressure and does not leak.
Refer to the tester instructions. The cap must relieve pressure at 110 kPa (16 psi) and must hold the rated pressure for 30
seconds without going below 75.8 kPa (11 psi). Replace the cap if it fails to fall within these limits.
IMPORTANT: Before installing the cap, examine the lower inside sealing surface in the filler neck to ensure that it is
perfectly smooth and free of debris. Also, inspect the cam lock flanges on the sides of the filler neck to ensure that they are
not bent.
a - Coolant recovery passage
b - Sealing surfaces
7. Install the cap on the reservoir or the heat exchanger.
Testing the Closed‑Cooling System
Testing Coolant for Alkalinity
!
CAUTION
A sudden loss of pressure can cause hot coolant to boil and discharge violently resulting in serious injury from burns. Allow
the engine to cool down before removing the coolant pressure cap.
The coolant should be changed per the maintenance schedule (refer to Section 1C ‑ Maintenance) and should be checked for
alkalinity at least once between change intervals. To check the coolant for alkalinity, proceed as follows:
1. Obtain pink litmus paper from a local source.
2. Allow the engine to cool, remove the pressure cap from the heat exchanger, and insert one end of the litmus paper into the
coolant.
3. If the pink litmus paper turns blue, the coolant is alkaline and does not need to be replaced.
4.
If the pink litmus paper remains pink, the coolant is not alkaline and must be replaced. Refer to Changing Coolant.
Pressure Testing the System
!
CAUTION
A sudden loss of pressure can cause hot coolant to boil and discharge violently resulting in serious injury from burns. Allow
the engine to cool down before removing the coolant pressure cap.
Models with Closed Cooling
Page 6C-12 © 2016 Mercury Marine 90-8M0099748 eng DECEMBER 2015
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