Iridium spark plugs use a very fine iridium center electrode, which is harder and has a higher melting point than platinum, so iridium plugs usually last longer and need slightly less voltage to fire. Platinum plugs are cheaper and also long-lasting; double-platinum plugs have platinum on both electrodes and are designed for waste-spark ignition systems. The right choice is usually the type your engine came with: upgrading from copper or platinum to iridium is generally fine, but downgrading from iridium to platinum shortens the interval.
Iridium vs platinum at a glance
| Platinum | Iridium | |
|---|---|---|
| Center electrode | Platinum disc or tip | Very fine iridium tip |
| Typical life | Around 60,000 miles | About 60,000 to 100,000+ miles |
| Ignitability | Good | Slightly easier firing from the fine tip |
| Price | Lower | Higher |
Single platinum vs double platinum
In a waste-spark system, each coil fires two plugs at once, and one plug fires with reversed polarity, which wears the ground electrode. Double-platinum plugs protect both electrodes, so they are specified for many waste-spark engines.
Do iridium plugs add performance?
On a healthy stock engine, switching plug types does not add meaningful horsepower. Iridium’s advantages are longer life, stable firing over that life, and easier starts. Performance and boosted engines often use iridium or specific colder heat ranges recommended by the engine or kit maker.
Heat range matters too
Heat range describes how quickly a plug sheds heat. Engines with superchargers or turbos often need a colder plug to avoid pre-ignition; follow the kit maker’s recommendation. See what does a supercharger do?
Gapping fine-wire plugs
Most iridium and platinum plugs come pre-gapped. If you must adjust the gap, bend only the ground strap and never pry against the fine center tip, which breaks easily.
Copper plugs
Copper-core plugs with nickel alloy electrodes conduct heat well and cost the least, but their electrodes wear fastest. Some older engines and some racing applications still specify them. In a modern engine that came with iridium plugs, copper plugs would need replacing far more often.
Signs you used the wrong plug
Misfires, rough idle or knock soon after a plug change can mean the wrong heat range, the wrong reach or an incorrect gap. Check the part number against the specification before looking for other problems; see engine misfire.
Which should you use?
- Use the type and heat range in your owner’s manual.
- Upgrading from copper or platinum to iridium is generally fine and extends the interval.
- For waste-spark systems, use double platinum or the iridium plug specified for them.
See how often to change spark plugs, bad spark plug symptoms and bad ignition coil symptoms.
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