Cooling System
Components
216
Components
Water Pump and Intakes
External water intakes mounted in the gearcase
housing collect water and must supply the inlet
side of the water pump with an unrestricted 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 on p. 365 for water
pump servicing.
Water Supply Tube
The water pump outlet connects with a water tube
and hose assembly located in the outboard’s mid-
section. O-rings seal the water tube to the water
pump housing. Hose clamps secure the water
supply hose to the water tube and a fitting in the
exhaust adapter.
Water supplied to the water tube provides all cool-
ing water to the cylinder block.
Exhaust Adapter
• Adapts the cylinder/crankcase assembly (pow-
erhead) 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.
Pressure Relief Valve
A pressure relief valve is used to control water
flow and operating temperature at higher speeds
(above approximately 2500 to 3000 RPM). The
pressure relief valve opens as water pressure
increases. Spring tension sets the opening pres-
sure.
Overheating: A restricted or faulty valve typically
results in HIGH SPEED overheating.
(Impeller key removed for clarity)
1. Water inlet
2. Water outlet
3. Seal
4. Plate
5. O-ring
000697
DSC02328
1. Exhaust Adapter
009259
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