What size is the drain plug on a Subaru Impreza?

If you're changing the oil on a Subaru Impreza, knowing the exact size of the drain plug is essential. The right socket size and thread pitch can make the difference between a quick job and a frustrating struggle. Subaru has used a few different plug sizes over the years, and missing this detail leads to stripped threads or oil leaks. Get it right the first time with accurate info tailored to your Impreza's generation.

Standard Drain Plug Size for Most Subaru Impreza Models

For the vast majority of Subaru Impreza models from the late 1990s through recent years, the oil drain plug size is M20 x 1.5. This means the threaded section is 20 millimeters in diameter, with a thread pitch of 1.5 millimeters. The head of the plug usually takes a 17mm socket. This is true for most non-turbo Imprezas, including base 2.0 and 2.5 liter engines.

While the size is consistent for most generations, it's always wise to double-check your specific model year. Subaru hasn't made dramatic changes in this area, but there are a few exceptions, particularly for turbocharged models and earlier generations.

Variations by Year and Engine

Although M20 x 1.5 is common, some older Imprezas and turbocharged WRX/STI models use a different size. For example, some first generation Imprezas (1993-2001) and certain EJ20/EJ25 turbo engines use a plug with a 14mm or 16mm thread diameter. The head size may still be 17mm, but the thread is smaller.

If you have an Impreza WRX, WRX STI, or a pre-2002 model, check your owner's manual or physically measure the plug before ordering replacement parts. Using the wrong size can lead to stripped threads in the aluminum oil pan, a repair no one wants to tackle in the driveway.

Socket and Wrench Size Needed

On most Subaru Imprezas, the drain plug head takes a 17mm socket or wrench. This includes nearly all non-turbo cars from the late 1990s through the 2020s. If you're using a socket wrench, a six-point 17mm socket is best, as it grabs the hex head securely without rounding off the corners.

Some turbo WRX/STI models and rare early Imprezas may use a 14mm or 19mm head. If you don't have your car's service manual handy, it's smart to bring both a 17mm and a 14mm socket to the job, just in case. Always crack the plug loose with the correct tool to avoid damaging the soft metal head.

Thread Pitch and Why It Matters

Thread pitch refers to the distance between each thread on the bolt. The standard pitch for Subaru Impreza drain plugs is 1.5 mm (designated as M20 x 1.5). If you use a plug with the wrong pitch, it won't thread in smoothly and can damage the threads in your oil pan, causing leaks.

Always match both the diameter (M20) and the thread pitch (1.5 mm) when ordering a replacement plug. Many aftermarket plugs fit other Japanese cars but may have a 1.25 mm pitch, which looks similar but won’t seat properly in a Subaru oil pan. Double-check packaging or online listings for compatibility.

Crush Washer (Gasket) Size and Importance

Each time you remove the drain plug, Subaru recommends replacing the crush washer (gasket) that seals the plug against the oil pan. The correct washer size for most Imprezas is 20mm inner diameter. This ensures a leak-free seal without over-tightening the plug.

Using the wrong washer size leads to drips or can even deform the oil pan. Subaru lists the part as 803916010, but you can also use any flat, soft metal washer matching the correct dimensions. Some aftermarket oil filters include a replacement washer in the box, which is a good sign of a quality kit.

Torque Specification for Subaru Impreza Drain Plug

Screwing in the drain plug too tightly is a common mistake. For most Subaru Imprezas, the official torque spec is 33 ft-lbs (44 Nm). This is tight enough to seal the washer but not enough to crush the soft aluminum threads in the oil pan.

If you don't have a torque wrench, snug the plug firmly with a 17mm wrench, but don't bear down with full force. Over-tightening is a main cause of stripped pans and oil leaks. If in doubt, spend a few dollars at a local shop for a quick torque check - it's cheaper than an oil pan repair.

How to Identify Your Subaru Impreza’s Drain Plug Size

If you're unsure about your Impreza’s plug size, you can check your owner's manual or look up the part number based on your VIN. The manual typically lists the thread dimensions, or at least the part number for the plug and washer. Alternatively, you can unscrew the existing plug and measure it with a caliper - measure the diameter of the threaded section and the thread pitch if you have a gauge, or take the plug to an auto parts store and match it up.

Dealerships and most independent Subaru specialists can quickly pull the right size for your year and engine. Online Subaru communities or parts sites are also packed with guides and photos for specific models and years, especially for WRX and STI variants.

Aftermarket and Magnetic Drain Plugs

Many owners choose to upgrade to a magnetic drain plug to help catch tiny metal particles in the oil. Most aftermarket plugs for the Impreza are also sized at M20 x 1.5 and fit the original washer and thread. Some cheaper magnetic plugs may use a slightly different head size, so always verify you have the right socket before installation.

If you’re considering a magnetic plug, stick with well-reviewed brands or Subaru-specific models. These are engineered to match the correct thread pitch and torque rating, minimizing risk of leaks or stripped threads. Don’t forget to replace the crush washer, even with an upgraded plug.

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