Why Spark Plug Replacement Matters
Spark plugs ignite the fuel-air mixture that powers your engine. As plugs wear, the gap between the center and ground electrodes increases, requiring more voltage to fire. Eventually, the ignition coil can't produce enough voltage for a reliable spark — leading to misfires, rough running, and ultimately, engine damage from unburned fuel washing the cylinder walls.
Staying on top of spark plug replacement is one of the most cost-effective ways to maintain engine health and fuel economy.
Replacement Intervals by Plug Type
Copper Core Spark Plugs
Replace every 20,000–30,000 miles (or approximately every 2–3 years for average drivers). Copper is the most conductive electrode material but erodes faster than precious metals. These plugs are common in older vehicles with standard ignition systems.
Platinum Spark Plugs
Replace every 60,000 miles. Platinum's hardness dramatically reduces electrode erosion, extending plug life. Single-platinum plugs have a platinum tip on the center electrode. Double-platinum plugs (used in some Ford and GM waste-spark ignitions) have platinum on both electrodes and last just as long.
Iridium Spark Plugs
Replace every 60,000–100,000 miles depending on the specific plug and manufacturer's recommendation. Iridium is the hardest electrode material, and the ultra-fine tip requires less voltage while resisting wear. NGK Laser Iridium and Champion OE Iridium plugs are engineered to meet or exceed OEM drain intervals.
Warning Signs You Need New Spark Plugs Now
Don't wait for your interval if you notice these symptoms — they indicate plugs that need replacement immediately:
1. Engine Misfires
A misfire feels like a stumble, jerk, or hesitation — especially under acceleration or load. Misfires are often accompanied by a Check Engine Light with a P030X code (where X is the misfiring cylinder number). Persistent misfires send unburned fuel into the catalytic converter and can destroy it.
2. Hard Starting
If your engine cranks longer than usual before starting, especially on cold mornings, worn spark plugs (or worn glow plugs on diesel engines) are often the culprit. The wider electrode gap from wear requires more voltage to fire.
3. Rough Idle
A rough, uneven idle that feels like the engine is "lumpy" or shaking is a classic sign of one or more cylinders not firing properly. This can also indicate a fouled plug from oil or carbon deposits.
4. Poor Fuel Economy
Misfires waste fuel. If your MPG has dropped noticeably and no other obvious cause exists, check your spark plugs. Replacing worn plugs can restore up to 30% of lost fuel economy in severe cases.
5. Sluggish Acceleration
Worn plugs reduce combustion efficiency, making the engine feel less responsive when you press the accelerator. This is especially noticeable when merging onto highways or pulling a load.
6. Visible Damage on Inspection
When you remove plugs for inspection, look for: excessive electrode wear (rounded or eroded tips), carbon fouling (black, sooty deposits), oil fouling (oily wet deposits), or cracked/damaged insulators.
Should You Replace All Plugs at Once?
Yes — always replace the full set. Even if only one plug tests bad, the others are the same age and will fail soon. Doing them all at once saves labor time and ensures consistent ignition across all cylinders.
Shop Spark Plugs at Texan Supply Company
Ready for a tune-up? Browse our full selection of spark plugs from NGK, Champion, ACDelco, and Autolite. We carry copper, platinum, and iridium plugs for virtually every car, truck, and SUV.