FAA Powerplant Written Practice Test

What determines the heat range of a spark plug?

1. Its physical size

2. Its ability to transfer heat from the firing end to the cylinder head

3. Its resistance to wear

4. Its length and thread design

The correct answer is: Its ability to transfer heat from the firing end to the cylinder head

The heat range of a spark plug is primarily determined by its ability to transfer heat from the firing end to the cylinder head. Spark plugs generate heat during combustion, and this heat must be effectively dissipated to prevent overheating, which can lead to pre-ignition or spark plug failure. A spark plug with a proper heat range will retain sufficient heat to keep the firing end clean from carbon buildup while also transferring excess heat away efficiently to the cylinder head, maintaining optimal operating temperatures. Factors like physical size, resistance to wear, and thread design may have some influence on the overall performance and compatibility of the spark plug with the engine, but they do not directly determine the heat range. The essential characteristic in defining the heat range is the spark plug's design in relation to its thermal conductivity, which affects how well it manages heat during operation.