Car Care

Those tiny bolts of lightning under your bonnet

spark plug 4 redo

When routinely servicing your vehicle, spark plugs are often parts that pop up as needing replacement. In general, it's recommended to replace spark plugs as part of preventative maintenance based on manufacturer's specifications. Luckily though, spark plugs 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 effected. In the worst case scenario it might not start at all. Spark plugs have a hard job and have to endure extreme heat and pressure within the cylinder.

Why do you need to replace your spark plugs?

Having a good spark is one of the fundamentals in petrol engines. You need fuel, spark, and compression to even start; and good spark is directly linked to the performance of the engine.

Probably one of the most noticeable things you may have experienced with a faulty spark plug would have been a misfire. This is when a spark plug should fire but it misses its opportunity, which will cause an engine to run unevenly and lack power. If a misfire is left for too long unburnt fuel can consequently 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 manufacture has chosen. Your AA Auto Centre experts will recommend the correct spark plug for your vehicle.

Here is a rundown of the most common sparkplugs…


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 with the shortest life span.


Iridium spark plugs 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, however one drawback is that these spark plugs can be costly. These spark plugs are advantageous too, particularly if a spark plug is in a very tricky spot for the technician to get to.

Single Platinum

A single platinum spark plug is similar to a copper/nickel spark plug, however its centre electrode has a platinum disc welded to the tip instead of only nickel alloy. Platinum metal lasts longer than nickel alloy, however like iridium plugs these can be expensive.

Double Platinum

Double platinum sparkplugs have platinum coatings on both the centre and ground electrodes. This makes this sparkplug durable and if your vehicle has a wasted spark ignition system this is a good spark plug for the job as these systems fire spark plugs more frequently.


These are not very common and feature silver-coated electrode tips. They are not as durable as iridium or platinum spark plugs. They are sometimes used in older European model and motorcycles.

When should I replace my spark plugs?

Manufactures have set intervals when they recommend spark plugs are replaced. Copper nickel spark plugs for example, which are the least durable, only need to be replaced at about 50,000 km. And more expensive spark plugs like iridium can last up to 160,000 km. 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 your vehicle’s service it is common to remove a spark plug and check its wear level. Your skilled technician will advise if your spark plugs have become worn, they may also recommend replacing spark plugs as a remedy for other issues you may be experiencing such as poor fuel economy or performance.

What are the benefits of replacing my spark plugs?

  • New spark plugs mean better combustion resulting in improved performance.
  • Enhanced fuel economy - misfiring spark plugs can reduce fuel efficiency by 30%.
  • Easier to start - new spark plugs can make a big difference if your vehicle is hard to start. Worn spark plugs may have been the reason your car was having trouble starting or flooding.
  • Reduction in fuel emissions - not only can new spark plugs save you on your fuel bill but also reduce air pollution by optimising the use of fuel delivered to the engine.

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Find out more on how the AA can help 

Vehicle experts you can trust

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