Spark plugs ignite the air-fuel mixture in each cylinder — worn plugs cause misfires, poor fuel economy, rough idle, and hard starting. Modern iridium and platinum plugs last 60,000–100,000 miles, but worn plugs are one of the most commonly neglected maintenance items. The electrode material determines both performance and longevity.
We evaluated electrode material (iridium vs. platinum vs. copper), firing tip design, heat range, anti-seize coating, and compatibility with direct-injection and turbocharged engines to find the best spark plugs of 2026.
What to Look For
- Iridium vs. platinum vs. copper: Iridium has the highest melting point and smallest electrode tip (0.4–0.6mm) for the most precise spark — the best choice for modern engines. Double-platinum is the OEM standard for most 2005–2015 vehicles. Copper plugs require replacement every 20,000–30,000 miles but deliver the most voltage in older high-compression engines.
- OEM match: Your engine is tuned for a specific plug gap, heat range, and electrode style. Using the OEM-specified plug or an exact-match replacement from NGK, Denso, or ACDelco is always safer than a generic plug with incorrect specs.
- Heat range: Stock heat range (as specified for your vehicle) is correct for street use. Going one range colder is only appropriate for modified engines running higher boost or nitrous. Running too cold a plug in a stock engine causes fouling.
- Pre-gapped: Most modern iridium plugs come pre-gapped to a standard measurement. Always verify the gap against your service manual — some applications require adjustment. Do not close an iridium or platinum tip by force; the fine tip breaks easily.
- Anti-seize: Quality plugs are coated to prevent seizing in the cylinder head threads. Never apply additional anti-seize to iridium or platinum plugs — it changes the torque-to-clamping relationship and can cause the plug to back out.
Our Top Picks
ACDelco GM OE 41-162 Iridium Spark Plug (2-Pack)
ACDelco GM Original Equipment iridium plugs are the exact OEM replacement for GM vehicles (Chevrolet, GMC, Cadillac, Buick). The fine-wire iridium tip provides excellent wear resistance and precisely timed ignition for up to 100,000 miles. Made to the same GM engineering spec as the factory plugs — zero compatibility guesswork. If you drive a GM vehicle and want to maintain OEM-level performance without dealer prices, these are the correct plugs.
NGK Iridium IX Spark Plugs (4-Pack)
NGK is the world's largest spark plug manufacturer and the OEM supplier for Honda, Toyota, BMW, and most Japanese and European vehicles. The Iridium IX uses a 0.6mm iridium center electrode and tapered ground electrode for superior ignitability, quicker throttle response, and improved fuel efficiency. Available in the widest range of heat ranges and thread sizes of any brand — if your vehicle has a spark plug, NGK makes the correct replacement. 100,000-mile service life.
Denso Iridium Power Spark Plugs (4-Pack)
Denso is the OEM spark plug supplier for Toyota, Lexus, and Subaru — meaning Denso Iridium Power plugs are the same or equivalent to the factory-installed plugs in most Japanese vehicles. The ultra-fine 0.4mm iridium center electrode (finest tip of any mainstream plug) delivers the most concentrated spark, improving combustion efficiency and throttle response. Best for Toyota, Lexus, Subaru, and Mitsubishi applications where Denso is the OEM supplier. 120,000-mile rated life.
Bottom line: ACDelco OE iridium plugs are the best choice for GM vehicles — exact factory fit at a fraction of dealer prices. NGK Iridium IX is the most versatile option for all other makes, with the widest fitment coverage and proven OEM-level quality. Denso Iridium Power is the top pick for Toyota, Lexus, and Subaru owners.
Frequently Asked Questions
How do I know when spark plugs need replacement?
Check your owner's manual for the recommended interval — typically 30,000 miles for copper, 60,000 for platinum, and 100,000 for iridium. Symptoms of worn plugs include: engine misfires (check engine light with P030x code), rough idle, poor acceleration, increased fuel consumption, and difficulty starting. Modern vehicles with direct injection can also develop carbon deposits on plug tips that require earlier replacement.
Can I use iridium plugs in an older engine?
Yes — iridium plugs work in any gasoline engine as long as the thread size, reach, hex size, and heat range match the OEM specification. In older engines designed for copper plugs, you'll notice improved throttle response and better fuel economy. Use the correct part number from NGK or Denso's fitment database, not a generic iridium plug.
Do I need to use anti-seize on spark plugs?
Most modern iridium and platinum plugs have a factory-applied nickel anti-seize coating on the threads — do not add additional anti-seize. Adding anti-seize changes the torque relationship and can result in over-torquing, which strips threads or cracks the ceramic insulator. Torque plugs to spec using a torque wrench.
