2021 Subaru Impreza 2.0L Oil Change — FB20 Boxer, 0W-20, Step-by-Step DIY Guide

I've done the oil change on my 2021 Subaru Impreza sedan more times than I can count at this point, and it's become one of my favorite DIY jobs — not because it's particularly exciting, but because it's so consistent. The FB20 horizontally-opposed boxer 4-cylinder is a compact engine, the drain plug is easy to reach, and the spin-on filter is right there next to it. Total time: 25–35 minutes. Dealers and quick-lube shops charge $85–$120 for this service. Your DIY parts cost: $35–$45.

Two things matter most on the FB20: using 0W-20 full synthetic (Subaru specifies this viscosity specifically for the FB-series boxer engines) and replacing the aluminum drain plug washer every single change. Subaru's genuine 803916010 washer is a soft aluminum crush washer — it's designed to deform and seal once, and reusing it is one of the most common causes of slow drain plug seeps on high-mileage Imprezas.

Engine and Oil Specs

Item	Spec
Engine	FB20 2.0L DOHC horizontally-opposed boxer 4-cylinder
Output	152 hp / 145 lb-ft torque
Oil viscosity	0W-20 full synthetic (Subaru genuine or equivalent API SN/SP)
Oil capacity	4.4 quarts (4.2L) with filter
OEM oil filter	Subaru 15208AA15A
Drain plug size	14mm
Drain plug torque	30 lb-ft (40 Nm)
Drain plug washer	Subaru 803916010 (aluminum crush washer) — replace every change
Oil change interval	6,000 miles (severe use) / 7,500 miles (normal use)

Note on interval: Subaru's recommendation for the FB20 is 6,000 miles for severe use and 7,500 miles for normal driving. There's no oil life monitor on the 2021 Impreza — you track it yourself.

Tools and Parts List

• Subaru 15208AA15A oil filter (spin-on)
• 4.5 quarts 0W-20 full synthetic (a single 5-quart jug covers the fill with oil left over)
• Subaru 803916010 aluminum drain plug washer
• 14mm socket (drain plug)
• Strap wrench or oil filter cap wrench (64mm for Subaru spin-on filter)
• Torque wrench (20–45 lb-ft range)
• Drain pan (5-quart capacity minimum)
• Ramps or floor jack + jack stands (the Impreza sits low — ramps are almost mandatory)
• Funnel and rags

Cost Comparison

Item	DIY Cost	Shop Cost
0W-20 full synthetic (5 qt jug)	$26–$34	—
Subaru 15208AA15A filter	$8–$10	—
Subaru 803916010 drain plug washer	$1	—
Total parts	~$35–$45	—
Labor	$0	$50–$80
Total	~$35–$45	$85–$120

You save $45–$80 every oil change. At Subaru's 7,500-mile interval, that's two services per year for most drivers — roughly $90–$160 in annual savings.

Step-by-Step Oil Change

1. Warm the Engine

Drive the Impreza for 5 minutes to warm the oil. Let it sit for 15 minutes after parking to cool slightly before you work on it.

2. Raise the Vehicle

The 2021 Impreza sits lower than most SUVs and trucks. You'll need ramps to get comfortable access to the drain plug and filter. Roll the front wheels onto ramps, set the parking brake, and chock the rear wheels.

3. Locate the Drain Plug and Filter

The FB20 boxer layout places the engine horizontally. The 14mm drain plug is on the driver's side of the oil pan, pointing downward and slightly rearward. The Subaru 15208AA15A spin-on filter is on the driver's side of the engine, just behind the drain plug, also pointing downward. Drain plug and filter are right next to each other — you can change both from the same position under the car.

4. Drain the Oil

Position your drain pan. Loosen the 14mm drain plug counterclockwise, then remove by hand. Allow 5–7 minutes for a full drain.

Remove the Subaru 803916010 aluminum crush washer from the drain plug and discard it. Running the old washer even one additional change is the most common cause of the slow seep that many FB20 owners discover at the next oil check.

5. Remove the Old Filter

Rotate the 15208AA15A spin-on filter counterclockwise to loosen — it typically comes off by hand if the previous service was done correctly. If it's stuck, use a strap wrench or a 64mm cap wrench.

6. Install the New Filter

Apply a thin coat of fresh 0W-20 to the rubber O-ring on the new Subaru 15208AA15A filter. Thread it on by hand until the gasket contacts the block. Turn an additional 3/4 turn by hand — no tools.

7. Reinstall the Drain Plug

Install the new Subaru 803916010 aluminum crush washer on the drain plug. Thread the plug in by hand. Torque to 30 lb-ft (40 Nm). The FB20 drain plug torque is higher than many 4-cylinder cars — follow the spec with a torque wrench.

8. Fill with Oil

Open the oil filler cap on the passenger side valve cover. Pour in 4.0 quarts first. Start the engine, let it idle for 60 seconds, shut off, wait 5 minutes, check the dipstick. The dipstick on the FB20 is between the two cylinder banks, accessible from above. Add remaining oil in small increments to bring to the "MAX" mark. Total capacity is 4.4 quarts with filter.

9. Start and Check

Start the engine. The oil pressure light clears within 3–5 seconds. The FB20 boxer sometimes makes a brief ticking noise at startup from the hydraulic lash adjusters pressurizing — this is normal and clears within 10–15 seconds.

Let the engine idle for 2–3 minutes. Slide under and check the drain plug and filter for any drips.

10. Record the Mileage for Next Service

The 2021 Impreza has no oil life monitor — write the current mileage and next service mileage on a piece of masking tape and stick it on the driver's A-pillar or above the driver's visor.

FB20 Boxer Engine Notes

The FB20 is Subaru's second-generation boxer engine. Oil consumption in some FB20 model years has been documented — the 2021 is a refined version that largely addresses this, but checking the dipstick between oil changes is good practice. For short-trip driving (under 5 miles), switch to the 6,000-mile severe-use interval.

For the complete 2021 Impreza service schedule, see the OwnerDrop maintenance schedules guide.

The 0W-20 full synthetic spec and drain plug washer discipline here are nearly identical to what I covered in the 2023 Hyundai Elantra 2.0L oil change guide. For a full overview of oil change techniques and when to adjust your interval, see the OwnerDrop oil changes guide.

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