Learn all you need to know about changing spark plugs, from when to do it to how much it will cost you to buy and have them installed in the UK.

What do spark plugs do?

Spark plugs are responsible for starting your car’s ignition system, they ignite air and fuel in the car’s cylinders to start the engine. The process begins when the fuel enters the cylinder from an intake valve and is then compressed by the piston into a smaller space where oxygen is also present; this creates heat which causes sparks from the plug, starting an explosion of gases which pushes down on the piston, creating power. 

When the electrical spark is produced, it ignites the air-fuel mixture within the combustion chamber of the engine. This ignition is what provides power for your car to run at optimal efficiency and performance levels. 

Spark plugs are key components of the ignition system, consisting of three parts; a metal threaded shell usually made of copper or nickel alloy, an insulated centre electrode, and a ground electrode. Without spark plugs, it would be impossible for your vehicle to start or run properly, as they provide the energy that starts up your car’s engine.

It's important for car owners to make sure their spark plugs remain in good condition at all times so that their engines can function optimally!

How many spark plugs are in a car?

Generally, cars have four to eight spark plugs, one for each cylinder. So, the number of spark plugs depends on the size and type of vehicle. 

However, since electric cars use a battery to power their electric motors and turn the car's wheels, no spark plugs are needed!

How often should spark plugs be changed?

Generally speaking, most modern cars should have their spark plugs replaced after 20,000-40,000 miles, or three years of use - whichever comes first. 

It's important to follow this timeline as spark plugs that are too worn can lead to decreased performance and reduced fuel economy. 

If you're unsure about when you need to replace your spark plugs it's always a good idea to consult with your local mechanic or refer to your owner's manual. That will give you specific instructions regarding how often the spark plugs in your car should be changed.

Why do spark plugs wear out?

Over time, spark plugs can wear out due to age, heat, and vibration caused by the engine running over a period of time. 

The timeframe for spark plug replacement can vary greatly depending on the manufacturer, model and year of your vehicle. Factors such as driving conditions or other environmental influences can also impact the duration of spark plugs. 

As your spark plugs become worn out, they will eventually fail to provide adequate ignition for the efficient operation of your vehicle’s engine. 

In order to maintain optimal performance it is important to replace worn-out spark plugs with new ones on a regular basis. This will help keep your vehicle running smoothly and efficiently while also reducing the risk of any potentially costly damages resulting from faulty ignition systems or other related problems.

How do you know if your spark plugs need changing?

If you notice any of the following symptoms in your car then your spark plugs might need changing: 

• Your vehicle is having difficulty accelerating 
• Your car’s performance has decreased 
• The fuel efficiency is suffering because the engine is having to work harder
• An increase in emissions due to incomplete combustion causes unburned fuel to be released 
• A rough idle or misfires at low speeds or while accelerating. 

What happens when spark plugs fail?

When spark plugs go bad, they can cause a variety of issues with your vehicle's performance. If a bad spark plug is not replaced, it can lead to further engine damage which can mean very expensive repairs.

How much does a spark plug replacement cost?

On average, a complete spark plug replacement in the UK will cost between £50 to £300 depending on the type of vehicle and the number of spark plugs. 

The cost of a spark plug replacement comes down to the type and model of your vehicle. Luxury vehicles may require more expensive parts than standard models, while certain older cars may require specialized tools or engines for repair. 

Here's an idea of average costs in the UK for spark plugs for different cars and makes.

Fiat 500 Spark Plug Replacement Cost - £70

Ford Focus Spark Plug Replacement Cost - £70

Toyota Spark Plug Replacement Cost - £65-70

Vauxhall Spark Plug Replacement Cost - £200-300

BMW 3 Series Spark Plug Replacement Cost - £150

Labour costs associated with replacing spark plugs can also vary depending on how long it takes a mechanic to complete the job. Some jobs might take longer due to difficult-to-reach locations in some engine compartments or tight spaces between components. 

What's more, new technologies like direct injection systems have made it harder for mechanics to access hard-to-reach spark plugs which could add extra time to an already lengthy repair process. Finally, different brands and types of spark plugs are available which can affect both parts and labour costs when replacing them.

If you’re worried about the costs of an expensive spark plug change, then Bumper could help. With Bumper you can split the cost of repairs into monthly payments, completely interest-free.

Are spark plugs worth changing?

Most definitely, by replacing your spark plugs you’ll get a whole host of benefits, including improved engine performance, increased fuel efficiency, and reduced emissions. 

This simple maintenance task will not only keep your car running smoothly but can also prevent more expensive repairs that could arise from neglecting to change the spark plugs. 

Compared to other repair costs, spark plug replacement is an inexpensive service that should be done regularly as part of your regular car servicing in order to ensure optimal performance from your vehicle.

Can I replace spark plugs one at a time?

No, if you are changing spark plugs, the full set needs to be replaced at the same time. 

Changing spark plugs one at a time will have a negative effect on your car’s engine, so it’s not worth the risk.

If you’re worried about the cost of paying for all your spark plugs to be replaced at once, then consider Bumper. Bumper splits the cost of car repairs into 0% interest monthly instalments!

Find a trusted partner garage.

What happens if you don't replace spark plugs?

If you don't replace your spark plugs, you’ll probably find that your engine continues to run less powerfully than before or takes longer to start. It will likely be due to misfiring cylinders caused by the worn-out spark plugs. Additionally, the increased friction between pistons and cylinders created by these misfires can cause accelerated wear and tear on other parts of the engine such as the piston rings and valvetrain components. 

Your vehicle will also consume more fuel in order to compensate for this decrease in efficiency, leading to higher fuel costs over time. Last but not least, because incomplete combustion is occurring within the cylinder due to worn-out spark plugs, emissions from your vehicle will increase dramatically as well - creating a potential hazard for both yourself and those around you if left unchecked. 

In some cases, prolonged use of old spark plugs can lead to serious engine damage if not taken care of immediately!

Can I replace the spark plugs myself?

Replacing your own spark plugs is generally not recommended unless you are an experienced mechanic. However, if you choose to do it yourself, make sure you take all necessary safety precautions and follow the steps outlined in your vehicle's manual.

Of course, it can be tempting to change your own spark plugs, the main advantage being cost savings and convenience; however, it requires skill and knowledge. If done incorrectly, it could lead to further damage or injury.

Will new spark plugs make my car run better?

New spark plugs will not necessarily make your car run better; however, they can improve engine performance and fuel efficiency if your old ones are worn out or damaged.

Other considerations for the car running better: In addition to replacing worn-out or damaged spark plugs, there are other things you can do to improve your car's performance, such as making sure your tyres are properly inflated and maintaining regular oil changes.

Check out our guide to safety checks you should be doing on your vehicle. 

Split the cost with Bumper 

Spark plug replacement is an important part of routine car maintenance that can help improve engine performance, and fuel efficiency, and reduce emissions, however, the cost of replacing car parts can put you off! 

Bumper knows car parts are often the last thing you want to spend your money on. Look after your car and your bank balance by splitting the cost or repairs into monthly instalments, interest-free. 

Join the Bumper community and get access to the best care for you and your car. Choose a dependable dealership and split your repair bill into monthly chunks. 

Author - Joseph Law

Joseph has been writing about cars for over seven years and writing for Bumper for over two, blending his passion for automobiles with a talent for storytelling.

Joseph has written about engineering and cars for Autozilla, Komaspec, and several engineering manufacturers. When he's not writing or tinkering with one of his five cars, Joseph dreams of owning an Alfa Romeo 33 Stradale.