2003 Johnson ST 55 HP WRL 2 Stroke Commercial Service Manual, PN 5005483, Page 125Get this manual
POWERHEAD ENGINE TEMPERATURE CHECK
ENGINE TEMPERATURE CHECK
Temperature Gun, PIN 772018, or digital pyrometer should be used to accurately determine the engine's operating temperatures
indicate 140 15F (60 rC) when checking at top of the cylinder head If engine temperature is not within this range, troubleshoot cooling system to determine problem
Increase engine speed to 5000 RPMAt 5000 RPM, the digital pyrometer must not indicate more than 120F (50C) If engine temperature exceeds 120F (50C), troubleshoot cooling system to determine problem
Temperature Gun
To achieve accurate and consistent readings, engine temperature must be gauged at the top of cylinder head
IMPORTANT: For the following engine operating temperatures and RPM figures to be correct, the inlet water temperature must be 70 10F (21 3C)