Subaru has earned a fiercely loyal following for a reason. From the snowy mountain roads of Colorado to the rainy streets of the Pacific Northwest, Subaru vehicles are known for their all-wheel drive capability, rugged dependability, and surprisingly long service lives. But like every car brand, Subaru engines can wear out, suffer damage, or fail  and when they do, owners face the familiar question: what's the smartest, most cost-effective way forward?

For many Subaru owners, the answer lies in sourcing a used Subaru engine a replacement powerplant pulled from a donor vehicle with miles still left to give. The used car engines market offers a wide range of Subaru options, from the beloved EJ-series flat-fours that powered everything from the Impreza to the Outback, to the newer FA and FB boxer engines that carry Subaru into the modern era.

But not all used Subaru engines are created equal. Some offer outstanding reliability and value. Others come with known issues that can turn a bargain into a costly mistake. This guide breaks down which used Subaru engine models are genuinely worth your money  and which ones require extra caution.

Why Subaru's Boxer Engine Layout Matters

Before diving into specific models, it's worth understanding what makes Subaru engines unique. Unlike virtually every other mainstream automaker, Subaru exclusively uses horizontally opposed "boxer" engines — also called flat engines — where the cylinders lie on their sides and the pistons move in opposing directions like a boxer's fists.

This layout gives Subaru vehicles a lower center of gravity (improving handling), better weight distribution, and excellent compatibility with the brand's symmetrical all-wheel drive system. It also means Subaru engines are highly distinctive — mechanics who know them well are specialists, and replacement parts are specific to this unique design.

The boxer layout also creates one of Subaru's most persistent challenges: head gasket leaks. The flat orientation of the engine puts the head gaskets under different stresses than in conventional inline or V-configured engines, and certain Subaru engine generations are notorious for head gasket failures. Knowing which engines have this problem — and which don't — is critical when shopping the used market.

1. EJ25 2.5L SOHC — The Workhorse of the Subaru Lineup

Found in: Outback, Forester, Legacy, Impreza (1996–2011)

The EJ25 SOHC (single overhead cam) is perhaps the most widely available used Subaru engine on the market today. It powered millions of Outbacks, Foresters, and Legacies over a 15-year production run, which means used examples are plentiful and affordable.

Why it offers value: The EJ25 SOHC is a simple, proven engine with a massive support network. Because it was used so extensively, parts are inexpensive, mechanics are familiar with it, and used examples can be found at almost every auto salvage yard in the country. For owners of older Outbacks or Foresters who need a budget-friendly replacement, this engine is often the most practical choice.

The head gasket issue — what you need to know: The EJ25 SOHC has a well-documented reputation for head gasket failure, particularly in the 1999–2004 production years. This is the single most important factor to investigate when sourcing this engine used. Always ask whether the head gaskets have been replaced and request documentation. Engines from 2005 onward used a revised multi-layer steel (MLS) head gasket design that dramatically reduced failures — prioritize post-2005 units where possible.

Verdict: Excellent value when sourced from a post-2005 vehicle with confirmed head gasket history. One of the best budget used car engines for older Subaru applications.

2. EJ25 DOHC (EJ257) — The Performance Favorite

Found in: WRX STI (2004–2021), Legacy GT, Outback XT, Forester XT

If you own a WRX STI or a turbocharged Legacy GT, the EJ257 is your engine. This is the high-output, twin-scroll turbocharged version of the EJ25 family — a DOHC unit that produces up to 305 horsepower in STI specification and has become legendary in the performance community.

Why it offers value: The EJ257 is a robust, overbuilt engine designed for high performance. When properly maintained and not abused, it can last well past 150,000 miles. Its forged internals (in STI spec) make it more capable of handling power than many comparable performance engines. On the used market, EJ257 engines from well-documented, well-maintained vehicles can be outstanding values — especially given what a new performance engine would cost.

What to watch for: Because the EJ257 is a performance engine, used examples must be evaluated with extra scrutiny. Many STIs and turbocharged Legacies have been driven hard, modified, or both. Always seek out engines with documented oil change history and ask specifically about knock sensor codes, rod bearing condition, and whether the engine has ever been opened or modified. Ring land cracking and rod bearing wear are the primary failure modes on high-mileage or abused units.

Verdict: Outstanding value for performance applications — but demands more due diligence than naturally aspirated alternatives. Source from documented, stock vehicles whenever possible.

3. EJ20 2.0L — Compact, Efficient, and Highly Reliable

Found in: Impreza, WRX (turbocharged), Forester, Legacy (primarily JDM and Australian market, some USDM applications)

The EJ20 is the 2.0L sibling of the EJ25 and in many respects a cleaner, more reliable engine. While less common in the North American market than the EJ25, EJ20 engines — particularly naturally aspirated SOHC versions — have an excellent reputation for longevity and simplicity.

Why it offers value: The naturally aspirated EJ20 SOHC largely avoided the head gasket issues that plagued the EJ25. It's a lighter, slightly simpler engine that responds well to consistent maintenance and is widely used in global markets, meaning parts support is strong. For owners of JDM-spec Subarus or performance builds requiring a solid base engine, the EJ20 is a compelling used engine option.

What to watch for: Availability in the U.S. used market is more limited than for the EJ25. Many EJ20 engines are imported from Japan (JDM engines), which can offer the benefit of lower mileage but requires careful verification of the import history and mileage documentation. JDM units typically come with 40,000–60,000 miles, making them attractive candidates for used car engines buyers seeking relatively fresh engines at moderate prices.

Verdict: Highly reliable and great value, particularly for those willing to source JDM imports. Among the cleanest used Subaru engine options on the market.

4. FB25 2.5L — The Modern Naturally Aspirated Standard

Found in: Outback, Forester, Legacy, Impreza, Crosstrek (2012–present)

Subaru introduced the FB-series engines in 2011 as the next generation of their naturally aspirated lineup. The FB25 replaced the aging EJ25 in most applications and addressed many of its predecessor's shortcomings — including the dreaded head gasket weakness.

Why it offers value: The FB25 is a modern, efficient engine with improved fuel economy, a revised cooling system, and a design that has proven significantly more resistant to head gasket issues than the EJ25. As FB25-equipped vehicles age into the 100,000+ mile range, used examples are becoming increasingly available at reasonable prices. For owners of 2012 and newer Outbacks, Foresters, or Crosstreks, the FB25 is the natural replacement choice.

What to watch for: Oil consumption has been reported on some FB25 units — particularly in earlier production years (2011–2014). Subaru issued a technical service bulletin (TSB) addressing oil consumption on affected engines. When sourcing a used FB25, ask about oil consumption history and check for any evidence of low oil levels causing damage.

Verdict: A strong modern replacement and the best used Subaru engine choice for 2012 and newer naturally aspirated vehicles. Addresses most of the EJ25's weaknesses with a more contemporary design.

5. FA20 2.0L — The Turbocharged Modern Performer

Found in: WRX (2015–2021), BRZ, Toyota 86/GR86 (in naturally aspirated form), Forester XT, Crosstrek Hybrid

The FA20 represents Subaru's modern turbocharged engine architecture. In WRX form (FA20DIT), it produces 268 horsepower and delivers a notably more refined driving experience than the older EJ series. In naturally aspirated form (shared with the BRZ and Toyota 86), it's a high-revving, engaging unit with a devoted following.

Why it offers value: The FA20 is increasingly available on the used market as early WRX and BRZ models age. It's a modern, direct-injection engine with strong performance credentials and good parts support given its shared use across multiple brands (Subaru and Toyota). For WRX owners needing a replacement, the FA20 offers contemporary performance at a fraction of new engine cost.

What to watch for: Like all direct-injection engines, the FA20 is susceptible to carbon buildup on intake valves. The turbocharged FA20DIT also requires consistent oil changes — turbocharger oil supply is one of the first things to suffer from neglected maintenance. Always verify the oil change history rigorously when sourcing a used FA20 from a WRX.

Verdict: Excellent value for modern WRX and BRZ owners. A well-maintained used FA20 can deliver years of strong performance. The best used Subaru engine option for 2015–2021 WRX applications.

Key Factors When Buying Any Used Subaru Engine

Regardless of which engine you select, these principles apply universally:

Always verify head gasket history on EJ-series engines. For any EJ25 engine — especially pre-2005 units — this is non-negotiable. A blown head gasket that went unaddressed can cause secondary damage to the block and cylinder head that makes the engine unworthy of purchase regardless of mileage.

Request compression and leak-down test results. A healthy Subaru boxer engine should show consistent compression across all four cylinders (typically 170–185 PSI for most naturally aspirated applications). Significant variation between cylinders indicates wear, damage, or gasket issues.

Ask about the donor vehicle's maintenance records. Subaru engines reward consistent oil changes with impressive longevity. An engine from a well-documented vehicle is worth significantly more than a mystery unit with unknown history.

Consider mileage relative to generation. EJ-series engines with under 100,000 miles are generally good candidates. FB and FA-series engines  being more modern have slightly better longevity profiles, and units with up to 120,000 miles can still represent excellent value.

Insist on a warranty. A reputable supplier of used car engines will stand behind their inventory with a minimum 90-day warranty. Anything less is a red flag.

Cost Overview: What to Expect to Pay

Prices vary by mileage, supplier, region, and market conditions. Always factor in installation labor — typically 6–12 hours for a Subaru boxer engine swap, depending on the model and shop.

Conclusion

Subaru builds vehicles with genuine longevity  and that durability extends to their engines. Whether you're keeping an aging Outback on the road with a budget EJ25 swap or breathing new life into a WRX with a fresh FA20, the used Subaru engine market offers real value for smart buyers who know what to look for.

The key is sourcing from a supplier you can trust. Moon Auto Parts carries a verified inventory of used Subaru engines across all major models and generations  with documented mileage, inspection standards, and warranty coverage to back every sale. When your Subaru needs a new heart, make sure you're putting the right engine in it.

Frequently Asked Questions (FAQ)

Q1: Which used Subaru engine is the most reliable?

The FB25 (2012–present) is widely regarded as the most reliable modern naturally aspirated Subaru engine, having addressed the head gasket issues of the older EJ25. Among older engines, a post-2005 EJ25 SOHC with confirmed head gasket replacement is also a solid choice. The EJ20 SOHC (particularly JDM-sourced units) is another strong contender for reliability.

Q2: Do all Subaru engines have head gasket problems?

No — this issue is primarily associated with the EJ25 SOHC from approximately 1999 to 2004. Post-2005 EJ25 engines used improved multi-layer steel gaskets that dramatically reduced failures. The FB-series engines (FB20, FB25) and FA-series engines largely eliminated this concern through redesigned cooling systems and updated gasket technology.

Q3: How many miles can a used Subaru engine last after installation?

With proper maintenance, a quality used Subaru engine can deliver an additional 100,000–150,000 miles or more. EJ-series engines in well-maintained vehicles are documented running past 250,000 total miles. Consistent oil changes every 5,000–7,500 miles are the single most important factor in maximizing longevity.

Q4: Is it worth buying a JDM Subaru engine?

JDM (Japanese domestic market) engines can offer excellent value — they typically come with lower mileage (40,000–70,000 miles) due to Japan's vehicle inspection system that encourages earlier turnover. However, always verify mileage documentation and purchase from a reputable importer. JDM engines are a popular choice in the used car engines market for Subaru applications.

Q5: What is the difference between EJ25 SOHC and DOHC? 

 The SOHC (single overhead cam) EJ25 is the naturally aspirated version used in Outbacks, Foresters, and Legacies — simpler, lower output, and more widely available. The DOHC (dual overhead cam) EJ25 — specifically the EJ257 — is the turbocharged, high-performance version used in the WRX STI and turbocharged Legacy/Forester models. It produces significantly more power but requires more careful sourcing due to the performance use history of donor vehicles.