Replace Spark Plugs: When, Why, and How to Do It Yourself

If your engine is coughing, hesitating, or you notice a drop in fuel economy, the spark plugs are probably the first thing to check. They’re cheap, easy to reach, and swapping them yourself can save you a few hundred pounds at the garage.

How to Tell Your Spark Plugs Need Replacing

Old plugs show clear signs. Look for a rough idle, trouble starting, or a noticeable loss of power when you step on the accelerator. You might also see the check‑engine light flash with a misfire code. If you’ve hit the mileage mark recommended by the manufacturer – usually every 30,000 – 60,000 miles – it’s time for new ones even if the car feels fine.

Another quick test is a visual inspection. Pull a plug with a spark‑plug socket, wipe it clean, and check the tip. If it’s black and sooty, blistered, or the electrode is worn down to the metal, replace it. A clean, light‑brown tip means the plug is still doing its job.

Step‑by‑Step DIY Replacement

Gather a few tools: a socket set with a 5/8‑inch spark‑plug socket, a torque wrench, and a gap gauge. Most modern plugs come pre‑gapped, but double‑check the gap in your car’s manual and adjust if needed.

1. Let the engine cool – hot plugs can burn your fingers.
2. Locate the plugs; on most front‑wheel cars they sit on the top of the engine under a plastic cover.
3. Disconnect the ignition coil or spark‑plug wire from each plug. Pull straight to avoid breaking the connector.
4. Use the socket to loosen and remove the old plug. Turn counter‑clockwise and pull gently. 5. Check the new plug’s gap and adjust with the gauge if required. 6. Screw the new plug in by hand first to avoid cross‑threading, then tighten with the torque wrench to the spec (usually around 13‑15 Nm). 7. Re‑attach the coil or wire, repeat for each plug, and close the engine cover.

That’s it – a 30‑minute job for most cars. Start the engine and you should feel a smoother idle and quicker response.

Why fresh plugs matter goes beyond just feeling good on the road. They help the engine burn fuel more completely, which improves fuel efficiency and reduces emissions. A bad plug can cause uneven combustion, leading to higher oil consumption and even damage to the catalytic converter over time.

If you’re unsure about the right plug type, check the owner’s manual or look for the specifications on the old plug. Most shops carry the correct replacement, and you can ask the staff at Northwich Tyres Centre for a quick match – they’ll also fit the plugs for you if you’d rather not DIY.

Remember, regular spark‑plug checks are part of good car maintenance. Pair the replacement with an air‑filter swap and a quick fuel‑injector clean for an even bigger performance boost. Your engine will thank you with a smoother ride and a happier fuel gauge.