Spark Plug Guide: Replace, Symptoms & Tips

Ever wonder why your car feels sluggish or why it coughs when you rev the engine? Most of the time the culprit is a spark plug that’s lost its bite. Spark plugs are tiny but they fire the whole engine, so when they start to fail you’ll notice it right away.

How to Tell Your Spark Plugs Need Changing

There are a few tell‑tale signs that tell you it’s time for a new plug. First, listen for a rough idle – if the engine shakes at a standstill, the spark isn’t even. Second, look for slow acceleration; a misfiring plug can make the car feel like it’s stuck in first gear. Third, pay attention to fuel consumption. Worn plugs let the engine work harder, so you’ll see the gas gauge climb faster than usual.

Another red flag is the check‑engine light. Modern cars log a misfire code when a plug isn’t delivering the right spark. If you get that warning, a quick scan will confirm whether it’s a plug problem or something else. Finally, inspect the plugs themselves. Pull one out (you’ll need a socket), and check the electrode tip. If it’s black, oily, or has a lot of carbon buildup, it’s past its prime.

Best Practices for Buying and Installing Spark Plugs

When you shop for replacements, stick to the specs in your owner’s manual. The heat range, thread size, and gap are all tuned for your engine. A plug that’s too hot will overheat, while one that’s too cold won’t fire reliably. Don’t be tempted by cheap, generic plugs – they may save a few bucks now but will cost you in performance and fuel.

Installation is simple but a few steps make it go smoothly. First, let the engine cool down; a hot engine can damage the new plug. Then, use a torque wrench to tighten the plug to the manufacturer’s recommended setting – usually around 18‑22 lb‑ft. Over‑tightening can crack the cylinder head, and under‑tightening lets the plug loosen and misfire.

After you’ve installed the new plugs, set the gap with a feeler gauge if the plugs aren’t pre‑gapped. A gap that’s too small reduces spark strength, while a gap that’s too big can cause the spark to miss entirely. Finally, start the car and listen. A smooth, steady idle means you’ve done it right.

Replacing spark plugs regularly (typically every 30,000‑50,000 miles, depending on the type) keeps the engine clean, improves fuel economy, and helps the car start reliably in cold weather. If you’re not comfortable doing it yourself, a quick visit to a local garage – like Northwich Tyres Centre – will get the job done in under an hour.

Bottom line: good spark plugs are cheap insurance for your engine. Keep an eye on the symptoms, change them on schedule, and you’ll enjoy a smoother ride, better mileage, and fewer surprise breakdowns.