Spark plugs are small, cheap and easy to forget — right up until your engine starts misfiring, stumbling or drinking more fuel than it should. For such a tiny part, they do a big job, and worn plugs cause problems well out of proportion to their size.
So how often should you replace spark plugs? It depends on the plug type: copper plugs often need changing around 30,000–40,000 km, while iridium and platinum plugs can last 80,000–100,000 km or more. Below we explain what spark plugs do, the signs they’re worn, and how to pick the right ones for your vehicle.
What spark plugs do
In a petrol engine, the spark plug delivers the spark that ignites the fuel-and-air mixture in each cylinder. That tiny, perfectly timed spark is what turns fuel into the power that drives your car. When plugs wear, the spark gets weaker and less reliable — and every part of how your engine runs suffers for it.
Signs your spark plugs are worn
- Rough idle or misfiring: A lumpy, uneven idle or a stumble under acceleration is a classic worn-plug symptom.
- Hard starting: Weak plugs make the engine crank longer before it fires, especially on cold Bega mornings.
- More fuel use: Worn plugs burn fuel less efficiently, so you fill up more often for the same driving.
- Loss of power or hesitation: If the car feels flat or hesitates when you accelerate, tired plugs could be the cause.
- A check-engine light: Misfires from worn plugs often trigger the engine light — worth a diagnostic scan to confirm.
Copper, platinum or iridium: which plug is right?
Spark plugs aren’t one-size-fits-all. The metal in the tip changes how long they last and what they suit.
- Copper: The most affordable, with a shorter service life. Good for some older engines, but they need changing more often.
- Platinum: Longer-lasting than copper and a common factory fitment on many modern cars.
- Iridium: The longest-lasting and most efficient option, ideal for newer engines and anyone who wants to change plugs less often.
The golden rule: fit the plug type and heat range your vehicle is designed for. The wrong plug can run too hot or too cold and cause problems, so check your handbook or ask us to match them for you.
Should you change them yourself?
On many engines, spark plugs are a genuinely doable DIY job with basic tools and a bit of care — the right gap, the right torque and working on a cold engine matter. On others, the plugs sit under intake parts or coils that make access tricky. If you’re comfortable under the bonnet, it’s a satisfying job. If not, there’s no shame in leaving it to a workshop.
How worn spark plugs cost you at the bowser
Spark plugs might be one of the cheapest parts in your engine, but worn ones quietly cost you money every week. When the spark gets weak, some of the fuel-and-air mixture doesn’t burn cleanly — so you’re paying for petrol that never turns into power. Fresh plugs often bring back smoother running and better economy straight away.
Worn plugs also make the engine work harder for the same result, which means more emissions and more strain on other ignition parts like the coils. Because the drop happens so gradually, you usually don’t notice until you fit fresh plugs and the car feels sharper again. On a vehicle that covers the long distances common out here, those small inefficiencies add up over a year of fuel bills.
Gapping and fitting: getting it right
If you’re changing plugs yourself, three things matter most: the right plug, the right gap and the right torque. Many plugs come pre-gapped, but it’s worth checking the gap against your vehicle’s specification with a feeler gauge before fitting.
- Work on a cold engine: Never remove plugs from a hot engine — you risk damaging the threads in the cylinder head.
- Don’t over-tighten: Too tight can crack the plug or strip the thread; too loose can cause a misfire. Use a torque wrench to the specified setting.
- Replace as a set: Fit all-new plugs of the same type together so the engine runs evenly.
Frequently asked questions
How often should I replace spark plugs?
It depends on the plug material: copper plugs typically last 30,000–40,000 km, while platinum and iridium plugs can go 80,000–100,000 km or more. Always check your owner’s manual for the recommended interval for your vehicle.
Can worn spark plugs cause higher fuel use?
Yes. Worn plugs produce a weaker spark and burn the fuel-air mixture less efficiently, so the engine uses more fuel. Fresh plugs often restore smoother running and better economy.
Should I replace all spark plugs at once?
Yes. Replacing them as a full set keeps the engine running evenly and saves you doing the job again in a few thousand kilometres when the next plug wears out.
Can worn spark plugs stop my car starting?
Yes. Badly worn or fouled plugs produce a weak spark that can make the engine hard to start, especially on cold Bega mornings. If your car cranks but struggles to fire, worn plugs are one of the first things worth checking.
Do diesel engines have spark plugs?
No. Diesel engines ignite fuel with compression instead of a spark, so they don’t use spark plugs. They do have glow plugs that help with cold starting, but that’s a different part — this guide is about petrol engines.
Can I fit a different type of spark plug to upgrade my engine?
You can move to a longer-lasting plug like iridium, but only within the type and heat range your engine is designed for. The wrong plug can run too hot or too cold and cause misfires or damage, so check the specification or ask us to match the right upgrade for your vehicle.
Get in touch
Due for a plug change, or not sure which type your engine needs? Call Parts4 Bega on (02) 6492 5212 or drop into 115 Gipps Street — we’ll match the right spark plugs to your vehicle from our Fuel & Ignition range and have them ready to go.