Spark plug from NGK; B 7HS; 1 piece; Ø14 x 12.7 mm; 20.8mm spark plug wrench

Heat degree

The degree of heat is expressed in numbers from 2 to 13, where a low number means warm and the spark plug has a larger surface that is exposed to combustion gases and where the heat is dissipated slowly and the insulating base is heated quickly.
A higher number means a smaller surface area that is exposed to combustion gases, the heat is dissipated more quickly and the insulation foot is heated more slowly.

If the wrong heat level is selected:

Heat level too high:
The temperature of the spark plug remains too low and a coating forms on the insulation foot that creates an electrical leakage path and misfires.

Heat level too low
The temperature of the spark plug becomes too high, causing premature ignition and abnormal combustion, which can melt the spark plug electrode with risk of piston and / or valve damage.