1980 Johnson 4HP Service Manual, Page 54Get this manual
CHECKING TEMPERATURE The motor checked for overheating with the use of the Markal Thermomelt Stik This is heat sensitive stick, similar to which melts contact with surface at specific temperatureThe motor is best checked when operating boat If this is not possibIerun the motor in test tank for at least five minutes, at maximum speed of 3000 Using 163 Thermomelt Stik, mark the side of the cylinder (preferabIy the plug carrying the serial number) with the Stik 00 NOT use the stick the cylinder head exhaust The center of the cylinder head the hp motor will normally run slightly hotter than 163 If the Stik will not leave mark the surface being checkedhold the Stik against the surface See Figure 5-2 The mark will dull and chalkyIf the mark melts and appears glossy, the powerhead is overheatingCheck for worn water pump clogged leaky cooling system (See Section 6, Lower Unit)
Oisconnect connectorsRemove spark plugsignition coils and flywheelRemove sensor, charge coil and plate assembIy as described in Section 4d If only upper main bearing seal replacement is required use Crankshaft Seal Removerlnstaller Part No391060See Figure