Cylinder Block / Cylinder Head Cooling
The flow of water through the cylinder block and cylinder heads is controlled by two thermostats and one external pressure valve. The pressure valve is connected by hoses to the top of the block and each cylinder head.
Thermostats
Pressure valve assembly
The thermostats and pressure valve control the flow of water entering the vertical water passages of the cylinder heads.
Water outlet passage at the bottom of each cylinder head aligns with a water outlet passage in the cylinder block. Water flows through the block to the adapter housing and then out of the outboard.
At low speed, the pressure valve is against the seat and the thermostats are closed. Warm water from the top of the cylinder block gradually migrates to the thermostat pocket at the top of each cylinder head. Water movement is the result of water “bleeding” past the pressure valve and thermostats.
The thermostat eventually opens as the water temperature in the system reaches 143°F (62°C).
When thermostat opens, increased water flow is directed down the cylinder head water passage to the water outlet passage of the block. Water then exits through the adapter/exhaust housing.
At higher speeds, water pressure increases. The pressure valve opens, or lifts off the seat, at approximately 2500 RPM. Water flows through the pressure valve and bypasses the thermostats. Hoses route the water flow from the pressure valve to the vertical water passages below the thermostats. All water flows through the cylinder heads to the outlet passages of the block and then exits through the adapter housing.
This pressure controlled water outlet circuit provides a “high flow” discharge of water during high speed operation.
This cooling system configuration provides “balanced cooling” at higher RPM by utilizing one pressure valve to control the discharge of water through both cylinder heads.
Refer to HOSE ROUTING AND WATER FLOW DIAGRAMS on p. 226.
Vapor Separator and EMM Cooling
Cooling water is routed from the top of the cylinder block to the inlet fitting of the EMM and through the EMM water cavity. Cooling of the EMM minimizes the temperatures of internal components.
Cooling water from the EMM is routed to the water inlet fitting of the vapor separator water cavity. Cooling the vapor separator fuel chamber minimizes fuel vaporization.
Cooling water from the vapor separator is routed to the water outlet fitting in the rear exhaust grommet.
IMPORTANT: Improper EMM cooling will activate service codes (code 29 and 25) and initiate S.A.F.E. or SHUTDOWN. Refer to EMM DIAGNOSTICS on p. 104 for specific service code information.
