2004 SR Johnson 2-stroke 40, 50HP Service Manual, Page 186Get 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
Start engine and run at 3000 RPM for at least five minutesReduce engine speed to 900 RPMAt 900 RPMthe digital pyrometer or Temperature Gun should 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 problemSTEP 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