1978 Johnson 55 HP Outboards Service Manual, Page 60Get this manual
PRESSURE VALVE
water jacket temperatures, the switch closes the warning horn circuitThe switch may be checked by submerging it in hot oilUse test light to check the contacts and thermometer to check oil temperatureThe contacts should close at temperature of 211 of (99C 3) and open at 175F(79C 4)See Figure 5-7
CHECKING MOTOR TEMPERATURE
WATER OUTLET WATER PUMP EXHAUST OUTLET The Markal Thermomelt Stik, heat sensitive stick similar to crayon which melts on contact with surface at specific temperature, is used to measure power head temperatureTwo Thermomelt Stiks are necessary to check motor125F (52C) Stik and 163F (73C) StikHold 125F (52C) and 163F (73C) Tempilstick on top of cylinder head with engine running less than 1000 R.P.Mand temperature stabilizedIf 125 (52C) Tempilstick melts and 163 (73C) Tempilstick does not, then thermostat is functioning properlyIf both melt, then engine is running too hotIf neither melt, then engine is running too coldRun engine at 4000 R.P .Mor more for several minutes and hold 125 (52C) Tempilstick on the top of the cylinder headIf 125F (52C) tempilstick melts, the engine is running too hot