2008 Evinrude E-TEC 55MFE Technical Manual, Page 180Get this manual
COOLING SYSTEM ENGINE TEMPERATURE CHECK IMPORTANT: If you get low or inaccurate readings with digital pyrometer, coat the probe location with Thermal Joint Compound, PN 322170 Pressure Relief Valve Inspection
The pressure relief valve should be closed at IDLE speedWater should not flow past the plunger and sealStart the outboard and check IDLE operating temperatureIf IDLE temperature is too low, check pressure relief valve plunger and seal for damage or debris that could prevent the valve from closing completelyIf IDLE temperature is still below operating range, replace pressure relief valve assembly and plunger sealTo test pressure relief valve operation, monitor temperature at the thermostat housing with Temperature Gun, PN 772018, or digital pyrometerConfirm normal IDLE operating temperatureSlowly increase engine speed from IDLE, up through 2500 RPMEngine temperature should decrease from normal IDLE temperatures as pressure relief valve opensValve should open between 1800-2200 RPMIf temperature decreases at lower RPM, replace pressure relief valve assemblyRefer to PRESSURE RELIEF VALVE SERVICING on p181