2020-2024 Subaru Outback - Spark Plugs Replacement

1

Cool the engine

The 2020–2024 Subaru Outback uses a BOXER engine — the spark plugs are on the SIDES of the engine, not on top. This is the defining quirk. 2.5L: NGK SILZKAR7B11. 2.4T: Subaru 22401AA92A. Gap: 0.044". Torque: 21 N·m (15.2 ft-lb) per FSM (older spec — verify for your year). You'll need: correct plugs for your engine (2.5L vs 2.4T differ), thin-wall spark plug socket, extensions, universal joint. Critical: let the engine cool — the boxer's aluminum heads are sensitive. The plugs are accessed from the sides, often through the wheel wells. This is NOT a top-access job like an inline-4.

🔧 Mechanic's note — Ray Delgado

Buy the plugs by engine — the 2.5L and 2.4T take different plugs, and I have seen the wrong box opened with the car already apart. NGK SILZKAR7B11 for the 2.5L; Subaru 22401AA92A for the 2.4T.

2

Access the ignition coils (from the sides)

Remove the engine cover. The ignition coils are on the SIDES — you'll access them from the side, by turning the wheels and going through the wheel-well liners, or from below. Remove any covers/airbox components blocking side access.

3

Remove one coil at a time

Remove ONE coil at a time. Unplug the connector, unbolt the coil, pull it straight out from the side. Inspect the boots. The tight side clearance is the challenge — use a universal joint on your socket extension.

4

Remove the old spark plug

Use your spark plug socket with extensions and a universal joint to remove the old plug from the side. The boxer's horizontal plugs can be awkward — the socket needs to go in straight. Don't drop debris into the open holes.

5

Gap and hand-thread the new plug

The new plugs come pre-gapped at 0.044" — verify but don't adjust (iridium). Hand-thread the new plug into the side-facing hole — this is tricky on the boxer because you're working horizontally. Turn by hand until it seats. NEVER force it — the aluminum heads strip easily, and the side angle makes cross-threading more likely. If it binds, back out and realign. The horizontal orientation means gravity isn't helping — be patient.

🔧 Mechanic's note — Tom Becker

I tell everyone in my shop to hand-thread those plugs with patience — the horizontal angle cross-threads easily and gravity is not helping. If it binds at all, back it out and start over; the aluminum heads do not forgive.

6

Torque to specification

Torque to 21 N·m (15.2 ft-lb) per the Subaru FSM (older spec — verify for your 2020-2024). Use a torque wrench with your extension/universal setup. The side-access makes torquing awkward — ensure the socket is fully seated on the plug. Do not over-torque — the boxer's aluminum heads are unforgiving. If your FSM shows a different value for the FA24F/FB25D, use that.

7

Reinstall the coil

Reinstall the coil — push it firmly onto the plug, bolt it down, reconnect the electrical connector. Double-check all coil connectors are clicked in — the boxer's side location makes it easy to miss one.

8

Reassemble and test

Start the engine — the boxer should idle with its characteristic rumble, smooth with no misfire. Check for codes (P0301-P0304). Test drive: the Outback should accelerate smoothly. The boxer's plugs are harder to access than an inline-4's — but the 0.044" gap and 15.2 ft-lb torque are straightforward once you're in. If you have a misfire, recheck the side-access coils — a loose connector on the far bank is the usual culprit. The 2.5L and 2.4T use different plugs — ensure you installed the correct ones.