1970 Johnson 1.5 HP Outboard Motor Service Manual, Page 33Get this manual
5-3 MOTOR
The motor checked for overheating with the use of the Markal Thermomelt StikThis is heat sensitive stick, similar to crayon, which melts contact with surface at specific temperatureThe motor is best checked when operating boatIf this is not possible, run the motor in test tank for at least minutes, at maximum speed of 3000 Using 163 Thermomelt Stik, mark the starboard side of the cylinder with the StikSee Figure 5-2
NOTE DO NOT use the stick the cylinder headThe center of the cylinder head the 1-1 motor will normally run slightly hotter than 163 FahrenheitThe mark will dull and cha1kyIf the mark melts and appears glossy, the power head is overheatingCheck for worn water clogged leaky cooling system(See Section 6, Lower Unit)REMOVAL OF POWER HEAD
Figure 5-2Checking Motor Temperature
SIX SCREWS3 PORT AND STARBOARD