Service Manual Evinrude E-TEC 40-60 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. 269 for water pump servicing.

001216
001217

1. Water inlet
2. Water outlet
3. Seal
4. Plate

IMPORTANT: The water pump housing includes a small hole to the rear of the water outlet. This hole provides cooling water for the tip of the exhaust passage. Be sure to use the correct parts when replacing the water pump.

004970

1. Hole

The water pump outlet connects with passages located in the outboard’s midsection. A grommet seals the water pump housing to the exhaust housing.

Water supplied to the exhaust housing provides all cooling water to the cylinder block.

A pressure relief valve is used to control water flow and operating temperature at higher speeds (above approximately 1800 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.

002437
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 lower speeds (below 1800 RPM).

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

Overcooling: Debris may prevent the thermostat from closing completely.

02439

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

Refer to THERMOSTAT SERVICING on p. 198.

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.

002478

1. Fitting

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

002461
1.Fitting

Cylinder Block / Cylinder Head Cooling

The thermostat is located in the top of the cylinder head. A separate pressure relief valve is positioned in the top of the cylinder block adjacent to the exhaust cover. The thermostat and pressure relief valve control the flow of water entering the vertical water passages of the cylinder head.

002441

1. Thermostat
2. Pressure relief valve

The controlled discharge of water from the thermostat and/or the pressure relief valve allows water from the top of the cylinder block to enter the cylinder head. Water flows down through the cylinder head and exits at the bottom of the cylinder head. The water outlet of cylinder head aligns with a water passage at the bottom of the cylinder block. Circulated water flows through the outlet passage of the block to the exhaust housing and then out of the outboard.

At low speed, temperature is thermostatically controlled. The spring loaded thermostat remains on a seat in the cylinder head. Water flows through the thermostat only when it is open. The thermostat opens at approximately 143°F (60°C).

At higher speeds, temperature is water pressure controlled. The pressure relief valve spring tension provides the proper “blow off” pressure. The valve lifts from the seat in the cylinder head at approximately 1800 RPM. Cooling water flows around the valve to achieve high speed cooling.