Seawater Pressure Test For Mpi Models; Seawater Aeration Test - Mercury MerCruiser Product Applications Manual

2. Zero the pressure gauge.
3. Connect the pressure gauge to the connection on the adapter.
4. With boat in the seawater and while underway, operate engine at 1000, 2000, 3000,
4000, and WOT while observing gauge.
5. Pressure should be steady and not exceed 17 kPa (2.5 psi). Check the following if
abnormal readings are obtained.
FLUCTUATING READINGS
• Pickup located too far forward or outboard on the boat, allowing air to enter system.
• Pickup located too close to propeller or some other object and picking up disturbed
seawater flow.
• Loose connection in the system allowing air to enter.
• Seawater inlet hose collapsing; wire reinforced hose not used.
EXCESSIVE PRESSURE READING
• Seawater supply components improperly sized.
• Seawater pickup not located on hull in an area with a solid, air-free flow of seawater.
• Excessive bends in seawater inlet hose.
• Seawater inlet hose collapsing; wire reinforced hose not used.

Seawater Pressure Test for MPI Models

IMPORTANT: MPI models must use the flow values as listed in Specifications, see
Seawater Supply Test Specifications.
IMPORTANT: The boat must be in the seawater for this test.
1. Connect an appropriate scan tool to the diagnostic connector.
2. Operate the boat and advance the the throttle to 4000 RPM.
3. Measure the seawater pressure. If seawater pressure does not meet specification,
seawater inlet plumbing changes are required.

Seawater Aeration Test

The engine cooling system must receive a solid, air-free stream of seawater in order to
operate effectively.
1. Install a piece of clear plastic wire-reinforced tubing in seawater inlet hose of seawater
pickup pump.
2. Operate engine from idle to WOT, while putting the boat through normal operating
maneuvers. Simultaneously, watch the seawater flow through the clear plastic tubing.
90-863758060 AUGUST 2006
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a - Diagnostic connector
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Cooling System
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