Spark Plugs

Spark plugs are perhaps right up there when it comes to being the most overlooked components in a car's engine maintenance routine, especially with longer and longer service intervals more commonplace in today's world. For many, it's only when the existing plugs start causing issues that their replacement takes place. When spark plugs aren't in good health, it can have a noticeable effect on your car's behaviour, drivability, efficiency and even general health and wellbeing.

As the name implies, spark plugs' sole reason for being are to provide spark energy so as to facilitate combustion inside your engine and ultimately drive your car down the road. They work when electrical energy provided by the engine's ignition system being triggered rises enough to bridge the voltage difference between the plug's central and side electrodes, ionising the air/fuel mixture between the electrodes and enabling the high-voltage spark to form, thereby igniting the mixture inside the cylinder's combustion chamber.

Spark plugs come in a MASSIVE variety of sizes, fitment, length, wiring terminal, insulator type, central and ground (side) electrode type etc., and are identified by alphanumeric codes; examples of such codes would be "BPR6ES11" for plugs made by NGK, "W20EPR11" for Denso items, or "WR6DC" for Bosch units. Which specific spark plug you will need is often listed in your car's owner's manual. While you can't just pick any old spark plug and whack it in, equivalent plugs from different manufacturers are usually able to be used in place of the originals and conversion tables exist online to identify equivalent plugs across various manufacturers.

Spark plugs can wear out in a number of different ways; simply from just age and usage, being fouled by either oil or fuel contamination, a build-up of carbon (or other) deposits, damaged or broken electrodes, faults due to incorrect installation or just general exposure over time to the hazardous environment that is an engine bay (heat, vibration, moisture ingress etc.).

One term you may encounter when replacing spark plugs is "heat range", the specific operating temperature the tip of the spark plug is suited to. A "hotter" plug is one that is a superior insulator and retains more energy in and around the electrodes, while a "colder" plug does the opposite, conducting heat away from the "business end" of the plug. For the vast majority of motorists the sensible route is to match the heat range of the standard plugs. Experimenting with heat ranges of plugs is more the domain of some classic cars, motorsport usage or for highly-modified vehicles chasing every last horsepower in conjunction with a dyno-equipped workshop etc.

Last, but not least, is a spark plug's "gap", the distance between the central and ground (side) electrodes which is measured to tenths of a millimetre(!). Too-small a gap means the spark being generated is too weak as it doesn't have enough room to form properly. Too-large a gap can mean the spark energy dies out before it travels between electrodes, also resulting in a weak spark (if at all!). There is a "happy medium" for plug gaps which results in efficient spark production and is usually identified by parts of the identifying code belonging to the plug recommended for your particular engine. Nearly all spark plugs come "pre-gapped" these days, but minor adjustments can be made by bending the ground (side) electrode to open or close the gap - use of feeler gauges or a dedicated plug gap measuring tool are highly recommended here!

Bonus Info:

Perhaps the most interesting thing about spark plugs, aside from the whole high-voltage spark energy deal, is that they can tell you a lot about how your engine is running. For example, if you remove a spark plug and the electrode end is an even brown colour, then your engine is probably working well. If it comes out covered in soot then your engine is likely running rather rich or could have a weak ignition system. If it's covered in oily deposits then your engine could be burning oil, experiencing excessive blow-by, has worn valve guides or your engine is badly worn - or all of the above. Should you remove a spark plug and the electrode end is badly damaged or even missing bits entirely, then there's a good sign the engine might be experiencing detonation, could have ingested a foreign object or something really, really bad has gone awry inside the engine. If in doubt, see a professional mechanic post-haste!

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Spark plugs are perhaps right up there when it comes to being the most overlooked components in a car's engine maintenance routine, especially with longer and longer service intervals more commonplace in today's world. For many, it's only when the existing plugs start causing issues that their replacement takes place. When spark plugs aren't in good health, it can have a noticeable effect on your car's behaviour, drivability, efficiency and even general health and wellbeing. Read More

Spark plugs are perhaps right up there when it comes to being the most overlooked components in a car's engine maintenance routine, especially with longer and longer service intervals more commonplace in today's world. For many, it's only when the existing plugs start causing issues that their replacement takes place. When spark plugs aren't in good health, it can have a noticeable effect on your car's behaviour, drivability, efficiency and even general health and wellbeing.

As the name implies, spark plugs' sole reason for being are to provide spark energy so as to facilitate combustion inside your engine and ultimately Read More

Spark plugs are perhaps right up there when it comes to being the most overlooked components in a car's engine maintenance routine, especially with longer and longer service intervals more commonplace in today's world. For many, it's only Read More

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