Your engine sets the interval

There is no single spark plug interval that fits every car. Intervals can differ by engine, even in the same model; Ram's 2026 Ram 1500 schedule, for example, lists two replacements for one engine and one for the others. Look in the maintenance schedule section of your owner's manual for a line such as "Replace the spark plugs" and the mileage next to it.

Check whether the interval is mileage-only or "miles or years, whichever comes first." In Ram's 2026 Ram 1500 schedule, for example, a footnote says the spark plug change interval is mileage based only and yearly intervals do not apply.

From the 2026 Ram 1500 Owner's Manual (Maintenance Plan and footnote 2), read November 3, 2026.

A real example: the 2026 Ram 1500 schedule

Three engines in the same truck, two different schedules:

From the 2026 Ram 1500 Owner's Manual (Maintenance Plan; the table runs to 150,000 miles; spark plug intervals are mileage based only), read November 3, 2026. We use one automaker's manual as an example; check your own owner's manual for your vehicle.

Warning signs not to ignore

These signs need a check regardless of the plug interval. The check engine light, also called the malfunction indicator light (MIL), is part of the OBD II system that monitors the engine and automatic transmission control systems. Using Ram's 2026 owner's manual as an example:

• A steady check engine light: some conditions, such as a loose or missing gas cap or poor quality fuel, can turn it on. Ram says the vehicle should be serviced if the light stays on through several typical driving styles.
• A flashing check engine light: Ram warns this means severe catalytic converter damage and power loss will soon occur, and immediate service is required.
• A pungent burning odor or light smoke: Ram says an out-of-tune engine or certain fuel or ignition malfunctions can cause the catalytic converter to overheat, and these signs may mean the engine is out of tune or malfunctioning and may need immediate service.

fueleconomy.gov adds that a check engine light could be something minor or a more serious problem that reduces fuel economy, increases emissions or leads to costly repairs later, so have the vehicle inspected when it comes on.

From the 2026 Ram 1500 Owner's Manual (Engine Check/Malfunction Indicator Warning Light; Fuel System Cautions) and Keeping Your Vehicle in Shape (fueleconomy.gov), read November 3, 2026.

Fuel can shorten plug life

Ram's manual notes that gasoline blended with MMT, a manganese-containing additive used in some gasolines to raise octane, reduces spark plug life and emissions system performance in some vehicles, and recommends gasoline without MMT. MMT is prohibited in federal and California reformulated gasoline. Ram also does not recommend fuel additives sold as octane enhancers.

From the 2026 Ram 1500 Owner's Manual (Fuel Requirements: Methylcyclopentadienyl Manganese Tricarbonyl; Fuel System Cautions), read November 3, 2026.

Spark plug service at Elgin Auto Sales & Service Center

We service all makes and models. We can look up your engine's spark plug interval, replace plugs on your manufacturer's schedule, and check a lit check engine light.

Our service department at 1200 E. Chicago St. in Elgin is open Monday to Friday 8 a.m. to 5 p.m. and Saturday 8 a.m. to 4 p.m., and is closed Sunday. Schedule service, see our service specials or get directions.