Spark Plug Heat Range

SPARK PLUG HEAT RANGE





If the center electrode holds too much combustion heat, the fuel/air mixture may be ignited by the hot electrode before the spark occurs - this is called pre-ignition. High plug temperatures also increase the natural erosion of both electrodes.

If the center electrode holds too little heat, fuel deposits can build up on the electrode and "foul" the plug so that it will mis-fire.

Spark plug heat range is determined by the size of the insulator: the longer the insulator, the less efficiently it can transfer heat - the short, thick insulator transfers heat well and will operate much cooler.

The correct spark plug for each car is determined by the manufacturer - the heat range requirement is influenced by the compression ratio and general operating conditions.