Parts for your 2020 Subaru Legacy-Sump plug washers

2020 Subaru Legacy sump plug washers — what they do and when to replace them

Yes, the 2020 Subaru Legacy uses a sump plug washer. Subaru’s technical literature specifies a crush-type aluminium drain plug gasket for both engines offered that year (FB25 2.5L and FA24 2.4L turbo). The Subaru Service Manual for the 2020 Legacy instructs replacing the drain plug gasket at each engine oil change, and the Subaru Genuine Parts catalogue lists a 16 mm aluminium gasket (commonly referenced as P/N 11126AA000, with some listings showing 803916010) for the oil pan drain. Those official sources make it clear the washer is fitted and intended as a single-use sealing part.

On the 2020 Legacy, the sump plug washer’s job is straightforward: it crushes slightly as the drain plug is tightened, creating a reliable seal between the plug and the alloy sump. That soft aluminium ring takes up microscopic imperfections, stops weeps and drips, and helps the plug clamp evenly without over-stressing the threads. It’s simple, cheap, and very effective when used as designed.

Best practice—per Subaru guidance—is to replace the washer at every oil change. Reusing a crushed washer can lead to a slow seep, a dust-and-dirt halo around the plug, or the temptation to over-tighten the plug to “make it seal”, which risks stripping threads. Sticking with the genuine-style 16 mm aluminium gasket is the tidy way to keep things leak-free.

• Replace the washer at each service when the engine oil is changed.
• Use a quality aluminium crush washer sized for Subaru’s 16 mm drain plug (genuine P/N often listed as 11126AA000 or 803916010).
• Clean the mating surface on the sump and the plug head before refitting.
• Tighten the drain plug to the specification in the Subaru service data—no need to swing off it.
• If the plug’s threads look tired or the flange is scored, replace the plug as well.

Copper washers exist, and while some techs use them, Subaru specifies aluminium on this model because it reliably crushes at the correct torque and matches the sump material nicely. If someone’s fitted a magnetic or aftermarket plug with an integrated seal, follow that product’s instructions, but for a stock 2020 Legacy the separate crush washer is the go. Keeping a couple of spares in the glovebox means no dramas come service time.

What size sump plug washer does a 2020 Subaru Legacy use?

It uses a 16 mm aluminium crush washer designed for Subaru drain plugs. Genuine parts are commonly listed as P/N 11126AA000 (with some catalogues showing 803916010). It’s a single-use gasket—fit a fresh one each time the oil is changed.

How often should the sump plug washer be replaced?

Every oil change. Subaru’s service guidance calls for replacing the drain plug gasket whenever the plug is removed. Reusing a crushed washer can cause seeping and may encourage over-tightening.

Can a copper washer be used instead of the aluminium one?

Subaru specifies aluminium for this model. While a correctly sized, quality copper washer may seal, the safest bet for consistent results is the genuine-style aluminium gasket. If anything other than aluminium is used, make sure the dimensions match and the seal is renewed at each service.