Four telltale signs signal a spark plug should be replaced: misfires or rough running, hard starting, reduced fuel economy, and visible wear or fouling on the plug.
Spark plugs ignite the air‑fuel mixture in each cylinder, and over time their electrodes wear, gaps widen, and deposits build up. That wear can weaken spark quality, impair performance, and raise emissions. Replacing worn plugs is a common maintenance task, typically guided by the vehicle’s current service schedule and the type of plug installed (copper, platinum, or iridium).
Four telltale signs to watch for
Before you replace components, look for these indicators that your spark plugs may be nearing the end of their usable life.
- Engine misfires or rough idle and hesitation: A misfire means one or more cylinders aren’t firing consistently, causing rough running, vibrations, or a stumble during acceleration.
- Hard starting or stalling, especially when cold: Worn plugs can struggle to produce a strong enough spark to ignite the air‑fuel mix, leading to extended cranking or stall‑like behavior.
- Poor fuel economy or reduced acceleration: Weak or inconsistent sparking can cause the engine to burn more fuel for less power, lowering miles per gallon and responsiveness.
- Visible wear or fouling on the plugs: Carbon or oil deposits, glazing, or a widened electrode gap and a damaged ceramic insulator indicate the plug is no longer performing reliably.
If you notice any of these signs, schedule an inspection. Replacing faulty plugs is usually quick and affordable, and delaying replacement can increase wear on ignition coils and downstream emissions systems.
Summary
The four clear signs that a spark plug should be replaced are misfires or rough running, hard starting or stalling, poor fuel economy or sluggish acceleration, and visible wear or fouling on the plug itself. Regular maintenance and adherence to the vehicle’s manufacturer recommendations help keep engines running smoothly and efficiently.
How do I know if my spark plugs need replacing?
Key signs include rough idling, sluggish acceleration, engine misfires, difficulty starting, and a noticeable drop in gas mileage. Spark plug lifespan varies significantly by type — copper plugs may need replacement every 25,000-30,000 miles, while platinum or iridium plugs often last 100,000 miles or more.
How long do spark plugs last in a Subaru Crosstrek?
30,000 to 60,000 miles
Subaru recommends specific intervals for changing your spark plugs to maintain peak engine performance and efficiency. You generally replace spark plugs every 30,000 to 60,000 miles, depending on your particular Subaru model and engine type.
What kills spark plugs quickly?
Pre-ignition can lead to heat building up in the combustion chamber causing the spark plugs to fail. In addition, if the cooling system isn't functioning correctly, it can cause the engine and spark plugs to overheat. This overheating can lead to the spark plug's electrode wearing out faster.
What spark plugs are best for Lexus?
- Motorcraft Iridium Spark Plug SP-580-X. Customize.
- NGK IX Iridium Spark Plug 93501. Customize.
- Bosch Double Iridium Spark Plug 96339. Customize.
- Bosch Iridium Spark Plug 8505. Customize.
- NGK Laser Iridium Spark Plug 96210. Customize.
- NGK IX Iridium Spark Plug 5464.
- NGK IX Iridium Spark Plug 3764.
- NGK IX Iridium Spark Plug 6619.