Below is a list of possible external influences on a spark plug's operating temperatures. The following symptoms or conditions may have an affect on the actual temperature of the spark plug. The spark plug cannot create these conditions, but it must be able to deal with all the levels of heat, otherwise performance will suffer and engine damage can occur:

    Air/Fuel Mixtures seriously affect engine performance and spark plug temps.

• Rich air/fuel mixtures cause tip temperature to drop, causing fouling and poor drivability.

• Lean air/fuel mixtures cause plug tip and cylinder temperatures to increase resulting in pre-ignition, detonation, and possibly serious spark plug and internal engine damage.

• It is important to read spark plugs many times during the tuning process to achieve optimum air/fuel mixture. Computer-controlled engine applications do a pretty good job of this with the various sensors that report back to the ECM.

Higher Compression Ratios and Forced Induction will elevate spark plug tip and in-cylinder temperatures.

• Compression can be increased by performing any one of the following modifications:

  • reducing combustion chamber volume (i.e.: domed pistons, smaller chamber heads, milling heads, etc.)

  • adding forced induction (Nitrous, Turbocharging, Supercharging)

  • camshaft change

• As compression increases, a colder heat range plug is required, as well as higher octane fuel and paying careful attention to ignition timing and air/fuel ratios are also necessary.

    Advanced Ignition Timing: Advancing timing by 10° causes plug temperature to increase by approximately 70°C to 100°C.

    Engine Speed and Load: Increases in firing-end temperatures and are proportional to engine speed and load. When traveling at a constant high rate of speed, or carrying/pushing very heavy loads, a colder heat range spark plug should be installed.

    The heavier your vehicle or greater the amount of work the engine sees (racing applications, construction trucks, vans, RVs & motorhomes, etc.), the more critical this becomes.

    Ambient Air Temperature:

• As air temperature falls, air density volume increases, resulting in leaner air/fuel mixtures. This creates higher cylinder pressures and temperatures that causes an an increase in the spark plug's tip temperature. Fuel delivery should be increased.

• As temperature increases, air density decreases, as does intake volume, and fuel delivery should be decreased.

    Humidity: As humidity increases, air volume decreases. The result is lower combustion pressures and temperatures, causing a decrease in the spark plug's temperature and a reduction in available power. Air/Fuel mixture should be leaner, depending on ambient air temperature.

    Barometric Pressure and Altitude:

• Affects the spark plug's temperature

• The higher the altitude, the lower the cylinder pressure becomes. As the cylinder temperature decreases, so does the tip temperature.

• Many tuners attempt to "chase" tuning by changing spark plug heat ranges.

• The real answer is to play with the jetting or air/fuel mixtures in an effort to put more air back in the engine.