The optimal temperature window
Spark plugs require a special temperature window in order to work optimally. The lower threshold of this window is a spark plug temperature of 450 °C, the so-called self-cleaning temperature. Starting from this temperature threshold, the carbon particles which have collected on the insulator tip are burned off.
If the operating temperature continuously lies below this point, electrically conductive carbon particles can collect, forming deposits until the ignition voltage flows over the carbon layer to the vehicle mass instead of forming a spark.
With a spark plug temperature of 850 °C or higher the insulator heats up so much that uncontrolled ignitions can occur on its surface, glow ignitions. Such uncontrolled, abnormal combustion can lead to engine damage.