Spark Plug Heat Range
Heat range describes how quickly a spark plug transfers heat from its tip to the cylinder head.
What is Spark Plug Heat Range?
A hot plug keeps its tip hotter, helping to burn off deposits. A cold plug sheds heat faster, which suits high-performance or tuned engines. Manufacturers number heat ranges differently. Plug colour after use can indicate whether the heat range suits the engine.
How it works
The length of the insulator nose decides how far heat must travel, which sets the tip temperature.
Why it matters for your car
A plug that is too hot can cause pre-ignition; one that is too cold can foul. Use the plug specified by the engine maker.
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