The energy needed to run an internal combustion engine originates in the ignition of a fuel and air mixture in the cylinders. The energy generated by this miniature explosion forces the pistons within the cylinders into motion. The vertical movement of the pistons is transferred to the crankshaft which, in turn, creates the rotational movement that ultimately reaches the drive wheels that grip the road and move the vehicle.
To ignite that fuel and air mixture and create that burst of explosive power requires the flash of electricity produced by a spark plug. At least that is true in petrol-powered vehicles. Diesel vehicles don’t use spark plugs. Instead, they use compression and heat to create the environment in which the fuel/air mixture combusts.
For petrol vehicles then, the small and inexpensive spark plug is vital. Without them, a car isn’t going anywhere.
Spark plugs are the business end of the ignition system – a system that starts with the battery – and are placed at the top of each engine cylinder. Electric current flows through them and arcs across a gap between two electrodes at their base. This is the spark that causes the fuel and air mixture to combust.
The gap between the two electrodes is set and measured precisely by the manufacturer for best performance. The electrodes do wear over time and, as they do, the spark plug becomes less reliable and will need to be replaced.
TYPES OF SPARK PLUGS
COPPER/NICKEL: The lowest-cost type is made from copper and nickel alloy. They are likely to wear out quicker than other types and require replacing more often.
PLATINUM: Offering good performance, the centre electrode on this type of plug has a platinum tip. Platinum is tougher than copper and nickel alloy and though platinum plugs are more expensive, they do have the advantage of a considerably longer lifespan.
DOUBLE PLATINUM: A step up again from single platinum plugs, double platinum plugs have both electrodes coated with platinum, making them more efficient and longer lasting.
IRIDIUM: The longest-lasting plug type is made from durable iridium. It is very resistant to erosion and requires less voltage to generate a spark.
HOW LONG DO THEY LAST AND WHAT CAN GO WRONG?
All spark plugs wear out over time. They can also become ‘fouled’ – a condition where carbon or oil deposits build up on the electrodes interrupting the spark ignition. They can also be damaged by overheating. They can last anywhere from around 20,000 – 30,000 kilometres for copper/nickel plugs to more than 100,000 kilometres for iridium and platinum plugs. Whichever type is installed, when spark plugs start to fail the symptoms are the same.
MISFIRE & ROUGH IDLING: As the plugs wear, the timing and ‘quality’ of the spark starts to fall. This affects the combustion and can lead to a rougher driving experience, misfires and a rough idling sensation.
IGNITION: Spark plugs are essential to getting a vehicle started. Should they be faulty, it may become difficult to kick the engine into life.
DECLINING FUEL ECONOMY & PERFORMANCE: Less efficient combustion caused by faulty spark plugs will lead to an increase in fuel consumption and a decline in a vehicle’s performance, especially in acceleration.
Spark plugs are relatively cheap components. Copper/Nickel plugs can be purchased for around $5 while double platinum ones can be as much as $40 each.
When it comes time to replace spark plugs, it should be remembered that a swap from one type to another is not recommended. Auto manufacturers design their vehicles with specific components in mind, including spark plugs, so it’s best to check if an upgrade to longer-lasting plugs is appropriate. A qualified mechanic can ensure that new spark plugs are installed correctly and are suitable for a vehicle.
WANT TO LEARN MORE?
MTA Queensland’s Vehicle Maintenance course is designed for those who are interested in gaining valuable information and learning good practices for everyday vehicle use. The result: a safer journey with fewer breakdowns and repairs. If you have ever wanted to learn how to carry out preventative maintenance, then this course is for you.
7 April 2020
Please note the information contained on this page is general in nature and does not take into account your specific needs or circumstances. You should consider whether the information is appropriate to your needs, and where appropriate, seek professional advice.