Although car engines are becoming increasingly complex bits of machinery, the basic mechanics remain the same, and petrol-powered combustion engines still rely on controlled explosions of energy to get them start.
Spark plugs are integral to this as they channel the electrical current from the ignition to ignite the air and fuel mixture within the cylinders, and it's this continuous ignition that keeps your car moving on the road.
If they're not regularly checked, cleaned and changed when necessary – usually, after every 12,000 miles – they can lead to problems such as trouble starting your car, poor acceleration and even high fuel consumption.
So if you're experiencing any of those problems, here's how to check and change your spark plugs in 6 easy steps…
1. Let the engine cool
If you've had the engine running, things can get pretty hot under the bonnet, so make sure you give the engine time to cool before you attempt any work. Now is as good a time as any to get your tools together. To change spark plugs you will need:
● A ratchet socket wrench (possibly with an extension bar)
● A spark plug socket (these usually come as part of a ratchet socket set)
● A spark plug gap gauge or feeler gauge
● New spark plugs
2. Locate the spark plugs
Take a look at your car's owner's manual to find where under the bonnet the spark plugs are located, how many you have and what size socket you'll need to remove them.
Generally, the spark plugs will be located where a bundle of wires leading to different points of the engine compartment converge. They'll most likely be protected by plug covers and you need to bear in mind you may have to remove an engine cover to see its inner workings.
Once you've located the plugs you should make sure you number the corresponding leads to the cylinder. This is so you don't confuse which lead goes where when you put in the new plugs.
3. Check for wear
It gets dirty under the bonnet quite easily, so plugs can be in perfect working order even if they are looking a little grimy. If, however, they have a white, limescale-type build up around the electrodes, the electrodes are missing, or there are signs of burning or a heavy build-up of soot, they will need replacing.
Note: If they are bent or broken, this could signify a mechanical fault in your engine and you should get your engine checked over by a qualified mechanic.
4. Remove the spark plugs
To remove a spark plug you should grip the wire plug as close to the bottom as possible, and gently work it off – never tug at it – to reveal the plug. Then you can fit your ratchet socket wrench to remove the spark plug from its housing.
Spark plugs fire in a specific order, so make sure you remove and replace them in the right order – getting them mixed up means the engine may stop running and can lead to greater damage.
Remove and replace the plugs one at a time, checking the gap in each to see if they are burnt out and need replacing. If you need to remove all of the plugs at once, mark each wire so you know which plug goes where.
5. Measure the gap to check if the plug needs replacing
Refer to your owner's manual to find out the optimum distance for your spark plug gap. It should be a specific measurement between .028-inch and .060-inch – armed with this info you can decide whether or not the plug needs replacing.
If it's completely burnt-out, put a new one in – if you have a plug with an adjustable gap it looks to be in good order but the gap is higher than it should be, you can try to change the gap by putting the gauge in between the plug gap and tapping it gently on a wooden surface until the measurement is correct.
6. Insert the new plugs
Before you insert the new plugs, check the leads for signs of wear or damage in case they need replacing. Use a wire brush or compressed air to clean around the wire connections to make sure they are clean.
When inserting the new plugs, put a dab of anti-seize lubricant on the plug threads and then tighten to about an eighth of a turn past hand-tight. Never over-tighten as this can damage the thread on the engine and lead to expensive and time-consuming repairs.
Once this is all done, replace the spark plug covers and, if applicable, the engine cover, drop the bonnet and get back on the road.
And you can dispose of the spark plugs with the rest of your household waste, no need for any specialist disposal and they're not really worth recycling.
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