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What is the heat rating of a spark plug?

By Li Chenyu / hcfire360 November

A spark plug must dissipate the heat produced by the combustion gases. The heat rating is a measure of the amount of heat dissipation.

It is essential to use a spark plug with a heat rating that matches a specific engine and its condition of use.

When a wrong heat rating is selected,
When the heat rating is too high,
The spark plug temperature remains too low and causes deposits to build up on the firing end; the deposits provide an electrical leakage path that possibly cause misfire.
When the heat rating is too low,
The spark plug temperature rises too high and induces abnormal combustion (pre-ignition); this leads to melting of the spark plug electrodes that could cause problems such as piston damage.