Service Manual 5007211_Evinrude E-TEC 75-90 HP Cooling System [Components]

All models use a two-stage cooling system design. The cooling system is dependent on water pump pressure and controlled by thermostat and pressure relief valve operation.

IMPORTANT: Restricted or inadequate water flow through the outboard reduces cooling system performance and may lead to severe powerhead damage.

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 stainless steel liner must seal against a separate stainless steel water pump plate.

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

• The bottom plate MUST seal to gearcase housing.

Refer to WATER PUMP on p. 262 for water pump servicing.

(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 adaptor housing. The water tube fastens to the base of the adapter housing with a retainer 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 megaphone and exhaust housings and the water tube.
• Provides water passages which route incoming and outgoing cooling water.
• Provides exhaust passages which connect to the inner exhaust of the outboard’s midsection.

1. Megaphone
2. Exhaust housing
3. Water tube
4. Adapter housing
5. Inner exhaust housing

A pressure relief valve is used to control water flow and operating temperature at higher speeds (above approximately 2000 RPM). Pressure relief valve activates or “blows-off the seat” as water pressure increases. Spring tension is used to set the “blow off” pressure.

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

Overcooling: Debris may prevent the valve from closing completely.

Pressure relief valve components

The pressure relief valve diaphragm allows the valve plunger to lift off the seat completely. This improves the self cleaning properties of the pressure relief valve.

The thermostat is used to control water flow and operating temperature at slower speeds (below 2000 RPM).

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

Overcooling: Debris may prevent the thermostat from closing completely.

1. Cover and O-ring
2. Spring and thermostat
3. Seal
4. Cylinder head

Refer to THERMOSTAT SERVICING on p. 199.

A fitting and hose connected to the top of the exhaust cover allows the constant movement of water and/or air from the block. Circulated water flows through the EMM and vapor separator before exiting through the overboard indicator.

1. Fitting

Fitting and hose for accessory water pressure gauge is connected at top of cylinder block adjacent to the pressure valve housing.

1. Fitting