Parts for your 2017 Subaru Legacy-Spark plugs

2017 Subaru Legacy spark plugs: purpose, care, and when to replace

Based on technical sources – the 2017 Subaru Legacy Owner’s Manual (Maintenance and Service schedule) and Subaru service manuals for the FB25 2.5‑litre and EZ36 3.6‑litre petrol engines – the 2017 Legacy/Liberty is fitted with coil‑on‑plug ignition and iridium spark plugs, with a specified periodic replacement interval. That confirms spark plugs are relevant and used on this model.

Spark plugs do the tiny but vital job of igniting the air–fuel mix inside each cylinder. Good plugs mean crisp cold starts, smooth idle, decent fuel economy, lower emissions and the full pull from that boxer engine when overtaking. Subaru specifies long‑life iridium plugs for the 2017 Legacy/Liberty, chosen because they resist wear and hold their sharp firing edge for far longer than old copper types.

For routine servicing, the factory schedule calls for spark plug replacement about every 96,000 km (60,000 miles) under normal driving. Short trips, dusty environments, or a lot of idling can justify earlier checks. Always replace the full set at once (four on the 2.5‑litre, six on the 3.6‑litre), use OEM‑equivalent iridium plugs (NGK or Denso as specified), avoid re‑gapping fine‑tip plugs, and torque to the Subaru service spec. Access is tight on a boxer under the bonnet, the job is doable for a confident home mechanic with wobble extensions and patience, but many owners will prefer a workshop to avoid cross‑threading the alloy heads. While you’re there, inspect coil boots and apply a dab of dielectric grease to keep moisture at bay.

• Typical signs your plugs are due: rough idle, sluggish take‑off, misfire under load, increased fuel use, harder cold starts, or a flashing check‑engine light (often with misfire codes).
• Good habits: check plug and coil condition around 50,000–60,000 km if the car does lots of short runs, keep the engine breathing well with a clean air filter, and fix any oil leaks that could foul plugs.

Note: In markets where a diesel Legacy existed, diesels use glow plugs rather than spark plugs. For 2017 AU/NZ Legacy/Liberty models, the engines were petrol, so spark plugs apply.

Popular questions about 2017 Subaru Legacy spark plugs

What’s the recommended spark plug replacement interval?
Subaru’s maintenance schedule for the 2017 Legacy/Liberty specifies about 96,000 km (60,000 miles) for iridium plugs in normal service. If the car sees frequent short trips, towing, dusty roads, or lots of idling, have them inspected earlier and replace if wear or fouling is found.

Which spark plugs should be used?
Use OEM‑spec iridium plugs from NGK or Denso as listed in the Subaru parts catalogue for your exact engine (FB25 2.5‑litre or EZ36 3.6‑litre). They come pre‑gapped, avoid forcing the gap on fine‑wire tips, and always torque to the service‑manual spec on a cool engine.

Can the plugs be changed at home?
Yes, with basic hand tools, quality plug sockets, wobble extensions and care. Access is snug on the boxer, so expect a bit of fiddling. If you’re not confident working around alloy heads and coil‑on‑plug gear, a professional service is a safe bet.