1972 Johnson 2HP Outboard Motor Service Manual, Page 33Get this manual
CHECKING MOTOR
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 temperaturemotor is best checked when operating boatIf this is not possible, run the motor in test tank for at least five minutes, at maximum speed of 3000 Using 163 Thermomelt Stik, mark the starboard side of the cylinder with the StikSee Figure 5-2
REFERENCE PICTURE
DO NOT use the stick the cylinder headcenter of the cylinder head the motor normally run slightly hotter than Fahrenheitmark 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)
Figure 5-2Checking Motor Temperature