AA CAR CARE: Tiny bolts of lightning
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Spark plugs often pop up as routine service items.
They should be part of preventative maintenance based on manufacturer's specifications, although luckily, they don’t wear out very quickly.
How they work
Spark plugs direct a controlled, tiny bolt of lightning during the combustion process. This is vital in the running of a petrol engine, without a good spark the engine will not run as smooth and its efficiency will be affected. In the worst case scenario it might not start at all. Spark plugs have a hard job, enduring extreme heat and pressure within the cylinder.
Why replace spark plugs?
A good spark is directly linked to the performance of the engine. One of the most noticeable things with a faulty spark plug is a misfire. This is when a spark plug should fire but it misses its opportunity, which causes the engine to run unevenly and lack power.
If a misfire is left for too long, unburnt fuel can damage sensors in the vehicle’s exhaust system.
What spark plugs do I need?
The main types of spark plugs are copper/nickel, iridium, single platinum, double platinum and silver. The correct plug varies depending on the vehicle and what the manufacturer has chosen. A technician can recommend the correct spark plug for your vehicle.
The centre electrode of this type of spark plug is copper core, coated with a nickel alloy. These are suitable for older vehicles and are the cheapest of the bunch, but also with the shortest life span.
These last the longest because iridium is harder and more durable. Many car manufacturers are now using iridium spark plugs so that the interval between changing them is much greater; but one drawback is that they can be costly.
A single platinum spark plug is similar to a copper/nickel spark plug, but its centre electrode has a platinum disc welded to the tip, instead of only nickel alloy. Platinum metal lasts longer than nickel alloy; but like iridium plugs, platinum can be expensive.
These have platinum coatings on both the centre and ground electrodes, making the spark plug durable. If the vehicle has a wasted spark ignition system, this is a good plug for the job because these systems fire spark plugs more frequently.
These are not very common: they feature silver-coated electrode tips and are not as durable as iridium or platinum spark plugs. They are sometimes used in older European models and motorcycles.
When should I replace my spark plugs?
Manufacturers have set intervals. Copper nickel spark plugs for example, which are the least durable, are replaced around 50,000km. More expensive spark plugs like iridium can last up to 160,000km. Of course, spark plugs can also fail prematurely; for example, if the insulation porcelain becomes cracked, the spark may fail to reach the combustion chamber.
During a service it’s common to remove a spark plug and check its wear level. A skilled technician will advise if the spark plugs have become worn, but may also recommend replacing them as a remedy for other issues such as poor fuel economy or performance.
What are the benefits of replacement?
- New spark plugs mean better combustion, resulting in improved performance.
- Enhanced fuel economy - misfiring spark plugs can reduce efficiency by 30 per cent.
- Easier to start. Worn spark plugs may have been the reason your car is having trouble starting, or flooding.
- Reduction in emissions - not only can new spark plugs save you on the fuel bill, they also reduce air pollution by optimising the use of fuel delivered to the engine.