Spark Plug: Description and Operation

Spark Plug Cutaway View:

PURPOSE
Spark plugs supply an air gap for secondary high-Voltage to arc across--igniting the air/fuel mixture in the combustion chamber.

NOTE: Platinum tipped spark plugs can be identified by blue lines on the ceramic insulator. Do not reuse them by cleaning or regapping. If platinum tip gap exceeds 0.050 inches.

HEAT RANGE
Spark plug heat range is determined by the plug's ability to dissipate the heat created during combustion.

Heat dissipation is affected by the length of the insulator around the center electrode, and the size of the heatsink area.
- The longer the insulator, the smaller the heatsink area--the hotter the spark plug tip.
- Hotter plugs tend to burn cleaner with less deposit build-up. They can be used for stop-start city driving, but are not recommended for extended high speed or high load conditions--as engine damage can occur.

Wrong Heat Range
- If a plug with too low of a heat range is used plug fouling will increase.
- If a plug with too high of a heat range is used preignition will occur.