Ever wondered what keeps your car’s engine humming along like a trusty old friend? Say hello to the handy spark plug.
Spark plugs ignite the air-fuel mixture in your petrol engine, creating the combustion needed to power your vehicle. But, like all good things, these little dynamos wear out over time.
Taking on the task yourself can save you a pretty penny, so in this guide, we’ll walk you through the process of changing your spark plugs safely and efficiently.
When should you change your spark plugs?
Different vehicles have varying intervals for spark plug replacement, so it’s always best to check your owner's manual for the specific schedule for your car.
Some manufacturers recommend replacing spark plugs as early as 30,000 miles. However, several signs may indicate the need for an earlier replacement. These signs include:
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Engine misfiring - if your engine is misfiring, it could be a sign that the spark plugs are worn out and not firing correctly.
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Loss of power - a noticeable loss of power when accelerating might be due to faulty spark plugs.
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Increased fuel consumption - if you’re finding that your car is burning more petrol than usual, it could be down to inefficient spark plugs.
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A rough ride - a rough or shaky ride, especially when idle, might indicate that your spark plugs require attention.
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The check engine light coming on - if your check engine light comes on, it could be a sign of many issues, including problems with your spark plugs.
Older spark plugs tend to seize in the cylinder head, making early replacement a wise move. Worn spark plugs can also lead to a noticeable decline in fuel economy, making your vehicle less efficient and more costly to run.
Why do spark plugs fail?
It's worth understanding the science behind why spark plugs wear out. Each time the spark plug fires, a small amount of the electrode material is lost due to the high temperatures and pressures inside the engine.
This erosion increases the gap between the electrodes over time, requiring more voltage to produce a spark. As a result, the engine can experience misfires and poor performance.
If the gap becomes too wide, the ignition system has to work harder to generate the spark, which can put additional strain on the ignition coils and other components. This extra strain can lead to further mechanical issues and even more costly repairs down the line.
Keeping an eye on your spark plugs and replacing them as needed is crucial for maintaining your vehicle's health and ensuring a smooth, efficient ride.
What tools do I need to change a spark plug?
Before you get busy replacing a faulty spark plug, you should gather the tools you’ll need for the job. Here’s your toolkit checklist:
Compatible spark plugs
First and foremost, you'll need a new set of engine plugs that are compatible with your vehicle. It's essential to buy high-quality or original equipment manufacturer (OEM) plugs, as cheap alternatives may not perform well and could cause engine issues.
Spark plug socket spanner
A spark plug socket spanner is designed to fit over the spark plug and remove it without causing damage. Make sure to use the correct size socket, preferably one with an internal gasket or magnet to avoid dropping the plug.
Torque wrench
A torque wrench will help you tighten the spark plugs to the manufacturer's specified torque setting. Over-tightening or under-tightening can cause damage, so this tool is essential for precision.
Extension bar (if needed)
An extension bar can help you reach spark plugs that are located deep within the engine bay. It's a handy tool to have in your arsenal for those hard-to-reach spots.
Feeler blades or a spark plug gap gauge (if needed)
These tools are used to measure and adjust the gap between the electrodes of the spark plugs. Ensuring the correct gap is crucial for optimal engine performance.
In addition to these tools, you may also want:
Anti-seize compound
Apply anti-seize compound to the threads of the new spark plugs to prevent them from seizing in the cylinder head over time.
Dielectric grease
Dielectric grease is used to lubricate the spark plug boots and prevent moisture from entering the connection.
Rags
Keep a few rags handy for wiping down tools and cleaning up any spills.
Masking tape and marker
Use masking tape and a marker to label the spark plug wires, ensuring you reconnect them in the correct order.
How to remove a spark plug
With all the tools acquired, it’s time to get stuck in. Let’s begin by looking at how to remove a spark plug:
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Safety first
Before you start, make sure the engine is cool before to avoid burns and potential thread damage. Disconnecting the battery is also a smart move to prevent any short circuits while working on the engine’s electrical system. It’s also a good idea to wear gloves and safety goggles for additional protection.
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Locate the spark plug
Locate the spark plugs using your owner's manual. Typically, they’re found on the top or side of the engine. In a 4-cylinder engine, spark plugs are usually in a row, while V6 and V8 engines have them evenly distributed on each side. Some cars may have engine covers that need to be removed to access the spark plug wires.
Clean the area around the spark plugs with compressed air to prevent debris from falling into the cylinder. Label any vacuum hoses you remove with masking tape and a marker. It’s also helpful to have a small magnetic tray to keep bolts and other small parts organised.
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Remove the ignition lead or coil
Ignition leads are thick, insulated wires attached to the spark plugs. Remove them one at a time to avoid confusion.
For coil-on-plug connectors, release the locking tab. Some systems may have a detachable rubber boot and spring that need removing.
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Remove the old spark plug
Use a spark plug socket spanner (with an extension if needed) to turn the socket anti-clockwise and loosen the plug.
If the plug is too tight, apply penetrating oil and stop before breaking the plug to avoid cracking it. Sometimes, gently warming the engine can help loosen stubborn plugs, but caution is needed to avoid burns.
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Inspect the plug
A normal used spark plug has a light brown or greyish deposit. White or oily plugs can indicate other engine issues, such as oil leaks or running too lean. Heavy, sooty build-up might also signal the need for replacement and could indicate running too rich or having a clogged air filter.
Consider photographing the old spark plugs before removing them entirely. The condition of the plugs can provide valuable diagnostic information about the overall health of your engine.
How to install a new spark plug
Now the old spark plug is out of the way, let’s look at how to install a new spark plug.
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Prepare the new plug
Most new spark plugs come pre-gapped, but it’s always good to double-check using feeler blades or a gap gauge. Refer to your vehicle manual for the correct gap measurement.
An incorrect gap can affect engine performance and fuel efficiency. Adjust the gap by carefully bending the ground electrode; using a gap tool ensures precision.
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Install the new plug
Apply a small amount of anti-seize lubricant to the threads of the new plug, particularly if installing in an aluminium engine. This helps prevent the plug from seizing and makes future removal easier.
Screw the new plug into the well by hand, turning it clockwise at least two full turns. This prevents cross-threading, which can damage the cylinder head.
Tighten the plug using a torque wrench to the correct torque setting as per your vehicle manual. Reduce torque by 10% if using anti-seize compound.
Correct torque is crucial to avoid blowouts or distortion. Over-tightening can crack the spark plug or the cylinder head, while under-tightening can result in a loose plug that can cause misfires.
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Reattach the ignition plug
Reattach the ignition lead or coil-on-plug connector, checking the plastic boot clicks into place. Use dielectric grease on rubber boots for easier future removal. Make sure it’s properly secured to prevent engine misfires.
If the lead or coil doesn’t click into place, the connection might not be secure, leading to potential engine performance issues.
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Final steps
Reinstall any parts removed to access the plugs and reconnect the battery. Start the vehicle and listen for smooth running.
If the engine runs roughly or the check engine light comes on, double-check your work to make sure that all connections are secure, and the spark plugs are properly installed.
Helpful tips
When it comes to changing spark plugs, a few handy tips can make the process much smoother and ensure you get the job done right. Here are some practical pointers to keep in mind:
Keep track of leads
It’s crucial to keep track of which lead attaches to which spark plug. Misplacing leads can cause your engine to misfire. Label each lead with masking tape and a marker if necessary. This simple step can save you a lot of hassle and guesswork later on.
Avoid abrasive cleaning
Never clean spark plugs with a wire brush or abrasive cleaner, as this can damage them. Instead, if the spark plugs are in relatively good condition, you can use a soft cloth to gently clean them. If they’re too dirty or damaged, it’s best to replace them.
Check for sooty plugs
Black, sooty spark plugs may indicate a clogged air filter. If you notice this, it’s a good idea to check and replace your air filter as well. A clean air filter ensures your engine runs smoothly and efficiently.
Replace damaged ignition leads
Inspect the ignition leads for any signs of wear and tear. Replace any leads that are cracked, oily, or damaged. Ignition leads are critical for delivering the electrical charge to the spark plugs, so keeping them in good condition is essential.
Use the correct spark plugs
Always use the correct spark plugs for your vehicle, preferably the same type currently in the car. Avoid downgrading to less expensive plugs, as this can affect your engine’s performance. Stick to high-quality or genuine parts for the best results.
Make sure the engine is cool
Before starting any work, make sure the engine is cool. Working on a hot engine can be dangerous and cause burns. Allow the engine to cool down completely before you begin.
By keeping these tips in mind, you’ll be well-equipped to change your spark plugs safely and effectively.
Find the right spark plugs at Hughie Willett Machinery
Changing spark plugs is a manageable DIY task that can save you money and improve your vehicle’s performance. If you need to find the right spark plugs for your vehicle, shop with Hughie Willett Machinery.
Check out our range today, or contact us for more information and advice.
Shop spark plugs at Hughie Willett Machinery today
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