Subaru Outback Spark Plugs: Intervals, Fitment & Warning Signs

A genuinely useful diagnostic technique: misting water over a suspected coil helps confirm it as the cause of a misfire — plus a warning that coils aren't interchangeable between vehicles, and using the wrong one can damage the ECU.

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OEM Part Numbers

Accuracy note: we weren't able to verify a confident Subaru Outback spark plugs part number at the time of writing. Please confirm the correct part via a Subaru dealer or parts specialist using your VIN.

A Cheap Part That Causes Expensive-Feeling Problems

Worn spark plugs rarely announce themselves clearly — a slightly rougher idle, a bit less punch off the line — symptoms easy to blame on almost anything else in the engine bay. The part itself costs very little, which makes it an easy one to overlook for far longer than it should be.

Before you buy: plug type and gap specification vary by engine size and generation. Always confirm against your VIN before ordering.

What They Do

Spark plugs ignite the compressed fuel-air mixture inside each cylinder, and their condition directly affects combustion efficiency, fuel economy and smooth running. Petrol engines rely entirely on them; diesel engines don't use spark plugs at all, relying on compression instead.

Generations & Spark Plug Count

Diesel variants, where fitted	Not applicable — diesel engines use compression ignition and have no spark plugs at all
Petrol variants (all trims, including WRX/STI)	4 spark plugs — Subaru's distinctive flat-four "boxer" layout is still a four-cylinder engine for plug-count purposes, just with the cylinders arranged horizontally in opposing pairs rather than in a line or a V

Subaru Outback Spark Plugs reference plate

A Genuinely Useful, Real Diagnostic Technique Worth Trying — Subaru Outback Spark Plugs

If you suspect a specific ignition coil is causing a misfire, this is genuinely worth trying: lightly misting water over the suspected coil with the engine running and watching whether it immediately stumbles or misfires is a genuinely practical way to confirm the coil as the cause. This works because water finding its way into a coil with a cracked casing or compromised connection can cause the spark to short and jump to the rocker cover instead of reaching the cylinder properly — a distinctive, testable symptom worth trying before committing to a full coil replacement based on guesswork alone.

A genuinely important warning worth knowing before sourcing a replacement coil: coil packs aren't simply interchangeable between different vehicles or even different engine variants, since a coil's inductance defines its charging time, and fitting the wrong one can result in a poor spark, a burnt-out coil, or worse, genuine damage to the coil driver circuits inside the ECU itself. It's worth confirming you're sourcing the exact correct part for your specific engine rather than assuming any coil of roughly the right shape will do.

It's also genuinely worth knowing an honest warning about parts sourcing: numerous documented reports describe counterfeit NGK spark plugs being sold through online stores, worth bearing in mind if a genuine-brand plug replacement doesn't resolve a misfire as expected. It's also worth knowing that a coil pack's epoxy resin developing visible cracks is a specific, real cause of misfires worth checking for directly — one owner replaced three of six coils on the same engine over time, with cracked epoxy confirmed as the cause on each occasion.

Warning Signs, DIY Difficulty & Aftermarket Advice

These are the same regardless of make or model — see our full Spark Plugs Guide for symptoms of worn plugs, why matching your exact plug specification matters, and trusted brands to buy from.

More Subaru Spark Plugs

The same part, covered across other Subaru models.

Subaru Outback Spark Plugs: Intervals, Fitment & Warning Signs

OEM Part Numbers

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A Genuinely Useful, Real Diagnostic Technique Worth Trying — Subaru Outback Spark Plugs