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Spark Plug Heat Ranges Explained & Cross Reference Table

Learn what a spark plugs heat range means & use our cross reference table

Using a spark plug with the correct heat range is critical for engine compatibility. To make things easier we've made this page to explain a few things, here you will find an explanation of heat ranges and how it can effect your engine, plus a cross reference table for heat ranges of some of the most common brands

What is a Spark Plug Heat Range?

Spark plugs heat ranges can vary massively from plug to plug, and (rather frustratingly) can be recorded in a number of different ways, making comparison between brands rather hard. Generally, if a plug has a hotter heat rating it's simply not as thermally resistant as a cooler graded plug. Low powered engines don't normally produce as much combustion warmth so won't heat up a plug as much or as rapidly as a high BHP vehicle, therefore the plugs have to be designed accordingly so they can reach and not exceed optimum operating temperatures. Commonly, you can spot a low heat range (or hot) spark plug as it typically has a long thin insulator nose which can heat up quickly / easily and will not dissipate warmth to the metal shell as rapidly, where as a high heat range (or cold) spark plug has a short thick insulator nose which will transfer heat much easier.

As a rule of thumb

  • Low power engines - low heat range (or hot) spark plug
  • High power engines - high heat range (or cold) spark plug

Heat Rating Too High

Although not as damaging as having a too low rated plug, the effects can still be detrimental to your engine. If a spark plugs temperature remains too low it can cause loss of ignition spark due to deposit build up on the firing end, which in turn will leave your engine struggling / down on power.

Heat Rating Too Low

This can be very damaging to your vehicles engine as the plug will overheat causing abnormal ignition firing (pre-ignition), that can lead to melting of the spark plug electrodes as well as piston seizure and erosion.

Heat Range Cross Reference Chart:

Ever wonder how spark plug heat ranges convert across brands? It can be a pain when you need a new spark plug but you don't know how your current heat range translate to a new brand. Well, below you will find a “heat range cross reference chart” that shows comparisons between 5 major brands of spark plugs.


If you need to know which spark plugs are suitable for your vehicle, simply use our handy spark & glow plug product lookup. Just enter your vehicle details to get started! Got a modified or track car? Not a problem, just give us a call on 01209 202 949 or use our custom recommendation form and we'll be happy to look into the best possible choice for you.

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Download - Using Spark Plugs To Health Check Your Engine