Evinrude & Johnson E75DPLSCB, Service Manual, Page: 197 / 349

195
COOLING SYSTEM
ENGINE TEMPERATURE CHECK
10
IMPORTANT:
If you get low or inaccurate read-
ings with a digital pyrometer, coat the probe loca-
tion with
Thermal Joint Compound , P/N 322170.
IMPORTANT:
Digital pyrometer or temperature
gun measurements may be slightly lower than
software temperature readings.
Idle Operating Temperature
Troubleshooting (Below Range)
If engine IDLE temperature is below operating
range 155°F ± 5°F (68.3°C ± 3°C), check thermo-
stat and pressure relief valve operation.
Thermostat Inspection
Check position of thermostat seal and how ther-
mostat seals against cylinder head. Seal must be
properly fitted to flange of thermostat.
Check thermostat for cracks, heat damage, or
signs of corrosion. Check for proper operation.
Thermostat opens at 143°F (62°C).
Refer to
THERMOSTAT SERVICING
on p. 196.
Pressure Relief Valve Inspection
The pressure relief valve should be closed at
IDLE speed. Water should not flow past the
plunger and seal.
Start the outboard and check IDLE operating tem-
perature.
If IDLE temperature is too low, check pressure
relief valve plunger and seal for damage or debris
that could prevent the valve from closing com-
pletely.
If IDLE temperature is still below operating range,
replace pressure relief valve assembly and
plunger seal.
To test pressure relief valve operation, monitor
temperature at the thermostat housing with Tem-
perature Gun, P/N 772018, or digital pyrometer.
Confirm normal IDLE operating temperature.
Slowly increase engine speed from IDLE, up
through 2500 RPM.
Engine temperature should decrease from normal
IDLE temperatures as pressure relief valve opens.
Valve should open between 1800-2200 RPM.
If temperature decreases at a lower RPM, replace
pressure relief valve assembly.
Refer to
PRESSURE RELIEF VALVE SERVIC-
ING
on p. 197.
Thermostat housing
002438
1. Thermostat seal 006401
1
1