Service Manual 5008740_200-300 HP 90 ° V Cooling System [Components]

External water intakes mounted in the gearcase housing collect water and must supply the inlet side of the water pump with a n un restricted and unaerated water supply. Water is drawn into the water pump through a hole in the lower plate of the water pump assembly. All cooling water to the powerhead is provided by the water pump.

• A nylon wedge (impeller key) is used to engage the impeller bushing and driveshaft.

• The nylon impeller housing with liner must seal against a separate water pump plate.

• The bottom plate MUST seal to gearcase.

• The pump operates as a positive displacement pump at LOW speeds (below 1500 RPM) and as a centrifugal pump at HIGHER speeds.

Refer to WATER PUMP SERVICE o n p. 292 for water pump servicing.

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(Impeller key removed for clarity)

1. Water inlet
2. Water outlet
3. Seal
4. Plate
5. O-ring

The water pump outlet connects with the water supply tube located in the outboard’s midsection. Grommets seal the water tube to the water pump housing and the inner exhaust housing.

On 3.3 L models, the water tube fastens to the inner exhaust housing with a water plate and screws.

Water supplied to the water tube provides all cooling water to the adapter housing and cylinder block.

• Adapts the cylinder/crankcase assembly (powerhead) to the exhaust housing and the water tube.

• Provides water passages which route incoming and outgoing cooling water.

• Provides exhaust passages which connect to the gearcase.

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1. Adapter housing – 3.3 L models

1. Adapter housing – 3.4 L models

A pressure relief valve is used to control water flow and operating temperature at higher speeds (above approximately 1200 RPM) . The pressure relief valve opens as water pressure increases. Spring tension sets the opening pressure.

Overheating: A restricted or faulty valve typically results in HIGH SPEED overheating.

Overcooling: Debris may prevent the valve from closing completely.

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Pressure Relief Valve Components

Thermostats control water flow and operating temperature at lower speeds (below 1200 RPM).

Overheating: A restricted or faulty thermostat typically results in LOW SPEED overheating.

Overcooling: Debris may prevent the thermostat from closing completely.

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Thermostat

A fitting and hose from the top of the block allows the constant movement of water an d/or air from the block. Circulated water flows through the EMM and Vapor Separator before exiting through the overboard indicator.