If the coolant section of the closed‑cooling 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 the pressure cap from the heat exchanger or the reservoir.
2. Clean, inspect, and pressure test the pressure cap.
3. Clean the inside of the filler neck to remove any deposits or debris.
4. Examine the lower inside sealing surface for damage. The surface must be perfectly smooth to achieve a good seal
between it and the rubber seal on the cap.
5. Ensure that the locking cams on the sides of the filler neck are not bent or damaged.
6. Adjust the coolant level to 25 mm (1 in.) below the filler neck.
7. Attach an automotive‑type cooling system pressure tester to the filler neck and pressurize the closed‑cooling section to
amount specified.
Pressure Cap Rating
Amount of Pressure Applied to Closed‑Cooling System
110 kPa (16 psi) 138 kPa (20 psi)
8. Observe the gauge reading for approximately two minutes; the pressure should not drop during this time. If the pressure
drops, proceed with the following steps until leakage is found.
9. While maintaining the specified pressure on the closed‑cooling section, inspect the external portion of the cooling system
(for example, hoses, gaskets, drain plugs, petcocks, core plugs, and circulating pump seal) for leakage. Also listen closely
for bubbling or hissing.
10. Test the heat exchanger.
Seawater Pressure Test
IMPORTANT: This test applies only to models with closed cooling.
IMPORTANT: The boat must be in the water for this test.
1. Connect the G3 diagnostic tool.
CDS G3 Diagnostic Interface Tool With
Harness
8M0046124
2. Start the engine. When the engine is at normal operating temperature, shift into forward gear.
3. Advance the throttle to 4000 RPM.
4. Check the seawater pressure with G3. If seawater pressure does not meet specification, further testing is required.
Description
Specification
Minimum pressure (models with closed cooling) 138 kPa (20 psi) at 4000 RPM
5. If no leakage could be found in the above steps, the engine is leaking internally. Leaking may be caused by one or more of
the following:
• Loose cylinder head bolts or damaged gasket
• Loose intake manifold bolts or damaged gasket
• Loose exhaust elbow or distribution block retaining nuts or damaged gasket
• Cracked or porous cylinder head or block
• Cracked or porous exhaust manifold
Proceed as follows until the location of the internal leak is found.
a. Start the engine.
b. Pressurize the system to the previously specified amount and observe the pressure gauge on the tester. If the needle
in the gauge vibrates, the compression or the combustion is leaking into the closed‑cooling section from a leak in the
combustion chamber.
c. Stop the engine.
d. Remove the spark plugs, examining each for the presence of coolant. A spark plug that is perfectly clean or has a
milky appearance is an indication of an internal leak.
e. Drain the oil from the engine and examine it for coolant. Oil will usually be milky if coolant is present. If coolant is
present, remove the engine from the boat and remove the oil pan. With the engine in the upright position,
repressurize the closed‑cooling section to the previously specified amount and examine the internal surfaces of the
engine to locate the leak.
f. If no leakage can be found in the above steps, the entire engine must be disassembled and inspected for leaks.
Models with Closed Cooling
90-8M0099748 eng DECEMBER 2015 © 2016 Mercury Marine Page 6C-13
To Next Page
Loading...
Need help?
General