Self FixerCom.DE

Engine Temperature check1988 Johnson/Evinrude 40HP - 55HP models

The Markal Thermomelt Stik is a heat-sensitive marker that melts on contact with a surface of a specific temperature. One source for Thermomelt Sticks is Stevens Instrument Company.

At least two Thermomelt Stiks or a 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 temperature. When the surface exceeds the Stik's rated temperature, the mark will appear liquid and glossy.

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^o 10^o F (21^o 3^o C).

Thermomelt Stik Procedure

1. Install correct test propeller and place engine in a test tank.
   Twist and remove spark plug leads before changing ill propellers to avoid accidental starting of engine.
2. Start engine and run at 3000 RPM for at least five minutes.
3. Reduce the engine speed to 900 RPM and mark the cylinder head with a 125^o F (52^o C) and a 163^o F (73^o C) Thermomelt Stik.
4. At 900 RPM the 125^o F (52^o C) mark should remain liquid and glossy. The 163^o F (73^o C) mark should remain dull and chalky.
   
   • If the 125^o F (52^o C) mark does not become liquid and glossy, troubleshoot the cooling system for causes of overcooling.
   • If the 163^o F (73^o C) mark becomes liquid and glossy, troubleshoot the cooling system for causes of overheating.
5. When the engine speed is increased to 5000 RPM, both marks should remain dull and chalky.
   
   • If either mark becomes liquid and glossy, troubleshoot the cooling system for causes of overheating.

Updated on: Wednesday, November 11, 2020