Start with your owner’s manual
The most reliable answer is the one from the vehicle’s manufacturer. Your owner’s manual or maintenance guide normally lists the recommended plug type or part number, the gap, and the replacement interval. Some cars also have an emissions label under the hood with plug information.
If the manual is missing, many manufacturers publish digital copies on their owner websites.
Use a part finder or ask the parts counter
Plug brands such as NGK, Denso, Bosch, Champion and Autolite offer online lookup tools. You enter your year, make, model and engine, and it returns compatible plugs. A parts store can do the same lookup.
Engine size matters. A model sold with more than one engine can need different plugs, so confirm the engine rather than just the model name. If the plugs in your car were already replaced by someone else, do not assume they are the right ones.
Spark plug types: copper, platinum, iridium
Plugs are commonly grouped by the material at the electrode tip.
| Type | General traits |
|---|---|
| Copper (nickel alloy) | Lowest cost and shortest life. Often used in older engines. |
| Platinum | Longer life than copper. Double platinum is often used in engines with a design that fires a plug on both the compression and exhaust strokes. |
| Iridium | A hard, durable metal. Often the longest-lasting option and standard on many modern engines. |
Lifespans differ by brand and engine, and published figures vary. For typical mileage ranges see how long spark plugs last and when to replace them. Prices also vary by brand and by store, so compare current prices rather than relying on a fixed number.
Specs that must match
Plugs are not interchangeable, even when they look similar. Check these against the specification:
- Thread size and reach: the plug must fit the cylinder head properly. A wrong reach can leave threads exposed or let the tip touch moving parts.
- Heat range: see spark plug heat range explained.
- Gap: the distance between electrodes. Many plugs come pre-gapped, but it is worth checking against your spec, and be gentle with fine-wire iridium and platinum tips.
- Seat type and hex size: needed for a correct seal and for the right socket.
Brand questions
Reputable manufacturers all make plugs that meet engine requirements when matched correctly. A common recommendation is to use the brand the vehicle came with, or a major brand’s listed equivalent. Whether one brand is “better” matters less than whether the part number is right for your engine. If you are weighing a specific line, such as Champion iridium, check that the listing matches your vehicle in the manufacturer’s part finder.
Mistakes to avoid
- Downgrading the material. If your car came with iridium plugs, replacing them with copper can shorten service life and may not suit the ignition system.
- Changing the heat range without a reason. Stick with the factory spec on a stock engine.
- Buying by price alone. The cheapest plug that fits is not necessarily the right plug.
- Skipping the gap check. Dropped or mishandled plugs can have a changed gap.
Signs it is time for new plugs
Typical signs include rough idle, hesitation, hard starting, a misfire and worse fuel economy. These can also come from other problems, so see bad spark plug symptoms and what you’ll notice. If you are weighing whether the job is worth the cost, our guide to spark plug and wire replacement can help.