When a plug becomes very hot in an engine, then it’s a hotplug. The plug that doesn’t reach a high temperature is a cold plug. The metal shell of each plug will function at almost the same temperature as the metal of the head itself because the plugs are screwed into the head and there is a good path for heat flow between shell and head.

Heat collected by the insulator tends to accumulate there because the insulator material is not a good conductor of heat. The track for heat flow is away from the insulator nose. Heat has to flow upwardly along the nose until it reaches the place where the insulator is in mechanical contact with the shell.

Plug

Spark plugs are manufactured with different heat ratings, from very cold to very hot, so a desirable plug can be found for your engine, depending on what you need, based on your riding or driving conditions. Plugs with the same diameter and reach will have different lengths of the insulator nose section and different type numbers to indicate which runs hot and which runs colder.

Also Read: Spark plug – Functions & Working

These plugs are mechanically interchangeable but will run at different operating temperatures in the same engine. Part of the tuning problem is to find a plug that survives in an engine.

What happens when the plug is too hot?