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.