What is the difference between iridium and platinum spark plugs on a Subaru?
Iridium plugs generally last longer and resist wear better than platinum plugs, while platinum plugs are usually cheaper and adequate for many daily drivers. For most Subaru owners, either type will work, but iridium is typically favored for longevity and reliability in modern or turbocharged engines.
Here’s a closer look at how the two materials compare, how Subaru engines respond, and what to consider when choosing between them.
What they are and how they differ
The following list outlines the practical differences you’ll notice in daily driving and maintenance.
- Material and electrode design — Iridium plugs use a very fine center electrode (often around 0.4 mm) made of iridium, which reduces wear and allows a tighter, longer-lasting spark. Platinum plugs use a thicker center electrode (around 0.7 mm) made of platinum, which also lasts longer than copper but wears more quickly than iridium.
- Durability and replacement intervals — Iridium plugs are typically rated for longer service life than platinum plugs. Many sources cite roughly 60,000–120,000 miles for iridium and about 60,000–100,000 miles for platinum, though actual intervals depend on the engine, driving style, and climate.
- Ignition performance — Iridium’s finer electrode can provide a more stable arc, especially at higher RPMs or under load, and may resist misfires a bit better over time. In normal, everyday driving, most drivers won’t notice a dramatic difference.
- Heat range and compatibility — Both materials come in various heat ranges. The key is to match the plug’s heat range to Subaru’s recommended specification for your specific engine. Using the wrong heat range can cause fouling or misfires, regardless of metal type.
- Gap retention and maintenance — Iridium plugs tend to hold their gap longer than platinum plugs due to their harder tip and design, but you should still verify the gap before installation and after any handling. Many plugs are shipped pre-gapped; always confirm the specification for your engine.
- Cost and availability — Iridium plugs are more expensive per plug but often offer longer life. Platinum plugs are cheaper upfront and can be perfectly adequate for many drivers when replacement intervals are kept in line with manufacturer recommendations.
Bottom line: if you value longevity and are driving a newer or turbocharged Subaru (or simply want fewer replacements over time), iridium is the premium choice. If you’re budget-conscious and have a vehicle that runs well on platinum plugs without frequent misfires, platinum remains a solid option as long as you follow the recommended maintenance schedule and heat range.
Subaru-specific considerations
The following notes help tailor the general differences to typical Subaru engines and driving scenarios.
Direct-injected and turbocharged engines
Subaru engines with direct injection (such as certain FA/FB designs) and turbocharged variants (like the WRX/STI line) often benefit from the durability of iridium, especially for high-load, high-RPM operation. Iridium plugs can maintain consistent ignition performance longer in these conditions, which helps reduce the risk of misfires as the engine ages.
Non-turbo, naturally aspirated engines
For many NA Subaru engines, platinum plugs remain a capable, cost-effective choice. If your driving is mostly routine commuting and you’re careful to follow the manufacturer’s replacement interval, platinum plugs can serve well without noticeable drawbacks.
Installation notes and maintenance
Regardless of material, use the engine-maker’s recommended heat range and gap. Do not force-fit a plug with an improper gap, and follow the official torque specification to avoid thread damage. In modern Subarus, many technicians avoid applying anti-seize on spark plug threads; rely on the manufacturer’s guidance and use proper torque with clean threads.
Summary
For Subaru owners weighing iridium versus platinum spark plugs, the most important factors are longevity, cost, and engine type. Iridium plugs offer longer life and potentially steadier performance under demanding conditions, making them a preferred choice for turbocharged or high-mileage engines. Platinum plugs provide reliable, economical performance for everyday driving when replacement intervals are kept reasonable and the correct heat range is chosen. Always consult your owner's manual or a trusted Subaru technician to confirm the correct heat range and gap for your specific model and engine family.
