What is the Spark Plug’s function?

The spark plugs are small but essential components to help start your vehicle. In an engine, there is a mixture of compressed air and fuel in each cylinder. The spark plugs deliver a spark to this fuel/air mixture in an internal-combustion engine, to ignite the fuel, creating a chain reaction of combustions that in turn drive the pistons & power the engine. In most petrol-powered vehicles, (you won’t find spark plugs in a diesel engine) the number of spark plugs is equal to the number of cylinders. However, some high-powered vehicles use two spark plugs per cylinder.

How do they work?

One end of a spark plug is rounded (called the terminal) and plugs into the wire head of the ignition lead/ coil, though which the electricity (provided by the ignition system when starting the vehicle) travels. An insulated centre electrode runs the length of the spark plug, with a hook-like appearance (the ground electrode) at the end. There is a space between the exposed centre electrode & the ground electrode. This is called the spark gap. The electricity travels through the centre electrode & jumps the spark gap, creating an arc of electricity, or small spark, that ignites the fuel/air mixture in the cylinder.

Different types of spark plugs

There are four main types of metals used in spark plugs for the centre electrodes. These are copper, platinum, double platinum & iridium. They all perform the same basic function, however the different materials have unique characteristics for various purposes, depending on the type of vehicle you drive. These metals act as conductors to channel the high voltage from the spark plug wire through the spark plug so it can cause the spark that starts the combustion process.


Copper spark plugs are the most common type & have a copper centre electrode. However, because copper is soft and has a low melting point, it is coated in a nickel-alloy outer-material to protect it. Previously the industry standard, they are typically found in older engines (pre 1980s). Copper is a more economical choice & they transfer heat fast. They also have the largest centre electrode of other spark plugs, resulting in more voltage required to generate a spark. Because the nickel-alloy coating is not as hard as other metals, they wear down quicker & need to be replaced more often; approximately every 40,000km.


Platinum spark plugs are similar to copper spark plug, but have a platinum centre electrode. Because platinum is a much harder metal than copper & has a higher melting point, it takes longer to deteriorate, resulting in an increased lifespan compared to standard copper spark plugs (about 100,000km). They can operate at a broader temperature range & generate more heat, which reduces carbon build-up. However, as you would expect, they come with a higher  price point.

Double Platinum

Whilst a platinum spark plug has a platinum centre electrode; a double platinum spark plug has a platinum on both the centre and ground electrodes. They are pricier, but offer another increase in both reliability, performance and longevity. They are recommended for a wasted spark ignition system (in which each ignition coil fires two spark plugs at once).


Iridium spark plugs are hyped as the best & most reliable type on the market. This type of precious metal is said to be six times harder & eight times stronger than platinum, with a 700° higher melting point. They contain a fine wire centre iridium electrode that provides an extremely efficient electricity conduction because they require less voltage in order to generate a spark. They also ignite faster & more efficiently. Iridium spark plugs are typically the most expensive type, but are very durable & can last up to four times longer than platinum/copper spark plugs. Iridium spark plugs are commonly found in high-performance engines & recently, more & more newer vehicles.

Which spark plugs are right for my vehicle?

You will need to consult with your mechanic or refer to your vehicle’s manufacturer’s owner manual to find out the recommended spark plugs for your specific vehicle. Just like with petroleum ratings; if the owner’s manual stipulates using iridium spark plugs; you cannot downgrade to platinum or copper, or you risk affecting the vehicle’s performance & causing potential engine damage. Alternatively, there is no benefit for installing more expensive spark plugs unless you have altered the engine after purchase.

What happens to spark plugs over time?

Spark plugs are made from material durable enough to ignite millions of times before wearing out. But, like anything, over time they will wear out. Here are some common things that occur to spark plugs over time:
  • Spark gap: Every time a spark plug creates an arc of electricity, it very minimally shortens the electrodes. Over time, the gap between the electrodes grows larger. As this gap increases, more electricity is needed to spark ignition of the air/fuel mixture. As this gap increases, the electricity won’t arc properly, and the engine will misfire. Eventually, the gap will grow so large that the spark plug won’t arc at all.
  • Carbon deposit/ build-up: Deposits from the air/fuel mixture can build up on the spark plugs over time, causing pre-ignition of the fuel which presents as a rough & unpredictable supply of energy to your vehicle.

How often should you replace spark plugs?

Spark plugs are very durable, however, it is normal for them to wear over time & eventually they will need to be replaced. Fewer kilometres on the odometer, regular scheduled maintenance, & keeping your engine in good condition can all prolong a spark plug’s life. Whilst driving habits such as driving at high speeds will wear the spark plugs at a faster rate. However, you should always consult your manufacturer’s recommendations. Typically, they will need to be replaced every couple of years, though it depends on the type of spark plug. They can last anywhere from 50,000km to 130,000km. Copper spark plugs have the shortest lifespan, while iridium can last up to four times longer. At Burleigh’s Mobile Mechanic we check the spark plugs at every Basic Service, & assuming they are still viable, we will then replace them at every Major Service.

Signs your spark plugs need replacing:

Without functional spark plugs, your engine will not start (there will be nothing to ignite the fuel and start the combustion process). However, there are some signs that your spark plugs are failing & need replacing. These include;
  • Reduced performance: When you are driving, your spark plugs fire when you accelerate & change gears. If the spark plugs are worn, your vehicle’s performance will be sluggish.
  • Poor fuel economy: Worn spark plugs can cause your engine to work inadequately, resulting in increased fuel consumption & emissions.
  • Engine misfire: When spark plugs begin to malfunction or wear, the spark may come too late or be too large, resulting in engine misfire.
  • Hard to start: If you are having difficulty starting your vehicle, worn spark pugs are the likely culprit.
  • Lack of acceleration: Your spark plugs not only send an initial spark that starts ignition, but also when your vehicle is accelerating. If your spark plugs are malfunctioning, the acceleration will feel slower & you might experience the engine stopping, stalling & then starting roughly again.
  • Unusual noises/ rough idle: When spark plugs are deteriorated & begin to misfire, it may cause strong vibrations or strange noises such as a knocking coming from the engine whilst idling.

Service you can trust

If you notice any of the above symptoms of spark plug failure, or have any issues with your vehicle, contact one of our friendly, qualified technicians today on 0412 161 776 for a vehicle inspection. It is important to replace worn spark plugs before they cause further damage to your vehicle. Spark plugs are also a good diagnostic tool for other issues with your vehicle. For example; black oily deposits on a spark plug can indicate an oil leak. Routine maintenance is critical to diagnose & fix any problems early; saving time & money further down the road. Don’t forget to like our  Facebook page for handy hints, information and special offers.