1974 Johnson 135 HP Outboard Motors Service manual, Page 53Get this manual
CHECKING ENGINE TEMPERATURE
The Markal The rmomelt Stik, heat sensitive stick imilar to rayon whi ch melts on contact with surface at specific temperature, Is used to measure power head tempe rature Two Thermomelt Stiks are necessary to check motor100 Stik and 130 FStikWith the motor at operating temperature, the 100 mark should melt nd the 130 mark hould not melt The motor is best checked when operating boatIf this is not possible, run the motor in test tank for few minutes, at speed between 3000 and 4000 rpmMark the top of both cylinder heads with the Thermomelt StiksThe marks will appear dull and chalkyWhen the 5urfaC'e temperature eaches the emperature ratings of the Stiks, the marks will melt, becoming liquid and glossy in appearanceOn some painted surfaces 011 whi ch the Stik will not leave mark, it will be necessa to hold the Stik against the su rface See Figure 5-7If the 100 mark does not melt after reasonable length of time, the thermostat is stuck open and the motor is unning too cold If the 130 mark also me lts, the cooling system is not fun ctioning properly, llowing the motor to overheatCheck Trouble Check Olart, Page 2-8