1991 Johnson/Evinrude Models "EI" 40 thru 55 Service Manual, Page 137Get this manual
Engine Temperature Check The Markal Thermomelt Stik is heat-sensitive marker that melts on contact with surface of specific temperatureOne source for Thermomelt Sticks is Stevens Instrument CompanyAt least two Thermomelt Stiks or digital pyrometer should be used to accurately determine the engine 's operating temperatures The Thermomelt Stik mark will appear dull and chalky when the surface marked is below the Stik's rated temperatureWhen the surface exceeds the Stik's rated temperature, the mark will appear liquid and glossy6469
To achieve accurate and consistent readings, engine temperature must be gauged at the top of cylinder head
For the following engine operating temperatures and RPM figures to be correct, the inlet water temperature must be 70 100 (21 30 e)
Pyrometer Procedure
"'" Avoid accidental starting of engine while changing propellers; twist and remove all spark plug leads