The FA20 Engine: A Performance Powerhouse with Known Weaknesses

The Subaru FA20 engine, a 2.0-liter direct-injected boxer four, first appeared in the 2012 Subaru BRZ and Toyota GT86 and later found its way into the 2015+ WRX. It is celebrated for its free-revving character, low center of gravity, and respectable torque curve. Enthusiasts appreciate the FA20's tunability, and on paper it delivers strong efficiency and power for its displacement. However, no engine is without its faults, and the FA20 has gained a reputation for two persistent issues: high oil consumption and boost leaks (especially in turbocharged variants). These problems can compromise reliability, reduce performance, and even lead to catastrophic engine failure if ignored. This guide explores the root causes of these common FA20 performance problems, provides thorough diagnostic procedures, and offers actionable solutions to keep your engine running at its best.

Overview of Common FA20 Performance Problems

While oil consumption and boost leaks are the primary focus, the FA20 can exhibit a range of performance-degrading issues. Early identification is critical. Beyond the two main topics, FA20 owners frequently report:

  • Cold-start misfires – often linked to carbon buildup on intake valves (direct injection lacks fuel wash) or faulty fuel injectors.
  • Timing chain noise – can indicate worn tensioners or guides, especially at higher mileage.
  • Overheating – often caused by a failing water pump, thermostat, or loss of coolant from leaks.
  • Excessive exhaust smoke – white smoke may point to a blown head gasket or cracked cylinder head, while blue smoke suggests oil burning.
  • Reduced power under load – frequently a direct symptom of boost leaks or a failing turbocharger/wastegate.

Addressing these issues early saves money and keeps your FA20 delivering the driving experience it was designed for. But let's drill down into the two most pervasive gremlins.

Oil Consumption on the FA20: Causes, Diagnosis, and Fixes

Excessive oil consumption is arguably the single most reported problem among FA20 owners, especially on naturally aspirated models. While some oil consumption is normal in any engine (Subaru officially considers up to 1 quart per 1,000 miles acceptable), many FA20s consume far more. Ignoring this can lead to low oil levels, oil starvation, rod bearing failure, and a complete engine rebuild.

Why the FA20 Burns Oil: Root Causes

The FA20's oil consumption stems from several design and wear-related sources. Understanding each helps narrow down the exact problem in your engine.

  • Worn or stuck piston rings: The FA20 uses low-tension piston rings to reduce friction and improve fuel economy. This design is inherently more susceptible to oil passing into the combustion chamber, especially if the rings become carbon-coked or fail to seal properly. Direct injection exacerbates carbon buildup on intake valves and can also foul ring lands.
  • Valve stem seal failure: As the engine ages, the rubber seals that control oil flow around the valve guides harden and crack. This allows oil to seep down the valve stem and into the cylinder, typically producing a puff of blue smoke on startup or after idling.
  • PCV (Positive Crankcase Ventilation) system issues: A clogged PCV valve, breather hose, or separator can cause excessive crankcase pressure. This forces oil past seals, rings, and into the intake tract where it is burned. On the FA20, the PCV system is known to clog over time, particularly in cars that see short-trip driving or infrequent oil changes.
  • External oil leaks: While technically not "consumption," oil leaking from cam carriers, the oil pan gasket, or the timing chain cover can mimic consumption and lead to low oil levels. These leaks can also drip onto exhaust components, creating smoke and fire risk.

Diagnosing Oil Consumption on Your FA20

Don't just top off the oil and hope for the best. A structured diagnostic approach is necessary to pinpoint the source of oil loss.

  1. Document oil usage: After an oil change, measure and record the oil level weekly. Drive a fixed distance (say 1,000 miles) and measure again. Do this for two to three intervals to establish a consumption rate.
  2. Look for external leaks: Use a UV dye and black light if necessary. Inspect the engine bay, especially the cam covers, oil pan, turbo oil lines (on FA20DIT), and the drain plug.
  3. Check for blue smoke: Smoke at startup suggests valve seals; smoke under acceleration or deceleration points to rings. A prolonged smoke test (idle, rev, coast) can help differentiate.
  4. Compression and leak-down test: A compression test reveals low cylinder pressure that could indicate ring or valve issues. A leak-down test quantifies leakage and can locate where it's escaping (e.g., air in crankcase = rings, air in intake/exhaust = valves).
  5. Inspect the PCV system: Remove the PCV valve and shake it – it should rattle. Check the breather hoses for clogs or cracks. On turbo models, the PCV system is more complex; look for oil in the intercooler piping as a sign of excessive crankcase pressure.
  6. Borescope inspection: Insert a borescope into the cylinder via the spark plug hole. Look for excessive carbon on pistons and valves, and for wet, oil-coated cylinder walls after the engine has been sitting.

Solutions: How to Address FA20 Oil Consumption

The remedy depends on the root cause. Start with the simplest and least expensive interventions before moving to major engine work.

  • Replace the PCV valve and clean the system: Often, a simple $20 valve replacement and a thorough cleaning of the breather hoses can reduce crankcase pressure and dramatically curb oil consumption. This should be step one for any FA20 burning oil.
  • Perform a hot engine flush: Use a high-quality engine flush product (e.g., Liqui Moly or BG) to dissolve carbon deposits stuck to the piston rings. Follow with an oil change using a high-quality synthetic with adequate ZDDP (important for flat-tappet cam engines). This can free stuck rings and restore sealing.
  • Replace valve stem seals: If compression and leak-down are good but you see smoke on startup, the valve seals are likely the culprit. This job requires removing the camshafts and can be done with the engine in the car, though it is labor intensive. A shop experienced with Subaru boxers can do it reliably.
  • Piston ring replacement (rebuild or short block): If ring wear is confirmed (low compression in a leak-down test, oil consumption above 1 quart per 500 miles), the only permanent fix is replacing the pistons and rings. Many owners upgrade to higher-tension rings from aftermarket suppliers like Manley or JE Pistons. Subaru has released updated piston ring designs for late-model FA20s; installing those can resolve the issue.
  • Check for oil leaks: Replace cam carrier gaskets, oil pan gasket, and any turbo oil or coolant lines. Use OEM or high-quality aftermarket seals and torque to spec.

Key external resource: For a deeper dive into FA20 oil consumption diagnostics, refer to Subaru's official technical service bulletins regarding the subject (search for TSB on oil consumption).

Boost Leaks on the FA20DIT: Symptoms, Detection, and Repair

For owners of the turbocharged FA20DIT (2015+ WRX and some Legacy/Outback XT models), boost leaks are a common enemy. A single small leak can rob the engine of 30-50 horsepower, cause lean fuel trims, increase exhaust gas temperatures, and trigger Check Engine Lights. Unlike oil consumption, boost leaks are relatively easy to fix once you find them.

Signs of a Boost Leak on the FA20

  • Noticeable power loss, especially in the mid-range: The car feels sluggish even though the turbo spools. Boost pressure may read low on the factory gauge.
  • Hesitation or surging during hard acceleration: A leak can cause the air-fuel mixture to fluctuate, leading to jerky power delivery.
  • Hissing sound under boost: A distinct air leak sound from the engine bay when under load. This is often most audible from the driver's window.
  • High fuel trims (Long Term Fuel Trim positive): A boost leak allows unmetered air into the engine; the ECU compensates by adding fuel. If your LTFT is above +10%, suspect a leak.
  • Check Engine Light with codes P0171 (lean), P0174 (lean bank 2), or boost-related codes like P0299 (turbo under boost).

Common Leak Points on the FA20DIT Boost System

Knowing where to look saves time. The FA20DIT's intake and charge air system has several vulnerable joints and components.

  • Intercooler couplers and hose connections: The plastic charge pipes that run from the turbo to the intercooler and then to the throttle body are secured with spring clamps. These can loosen over time, especially with increased boost from aftermarket tuning. Cracks in hoses also occur.
  • Intercooler core itself: The factory top-mount intercooler (TMIC) is prone to leaking at the end tanks after thermal cycling. An impact or pressure from a tune can also split the plastic end tank.
  • Throttle body gasket: The gasket between the throttle body and the intake manifold can fail, especially if the manifold has been removed and reused without a new gasket.
  • Turbocharger to downpipe connection: While not a charge air leak, a leak at the exhaust side can show as a boost leak diagnostic because it reduces exhaust flow to the turbine, spooling slower.
  • Evap system lines: The EVAP purge solenoid and lines connect to the intake manifold. If these lines crack, they introduce a vacuum/boost leak.
  • Wastegate actuator or diaphragm: A torn wastegate actuator diaphragm can cause uncontrolled boost. This often presents as erratic boost pressure and can be misdiagnosed.

How to Properly Diagnose Boost Leaks

Do not just tighten clamps and hope. Use a systematic approach with the right tools.

  1. Visual inspection: With the engine cold, check all hoses for cracks, loose clamps, and signs of oil residue (blow-by residue around a leak point). Pay special attention to the charge pipe from the compressor outlet.
  2. Smoke test: A professional smoke machine introduces smoke into the intake system under low pressure. Smoke will billow out of any leak. This is the gold standard and can locate even the smallest leaks. Many independent shops offer this service.
  3. Boost leak tester (pressurization): A DIY or aftermarket boost leak tester replaces the MAF sensor tube or turbo inlet with a fitting that connects to an air compressor. Seal the system and apply 10-15 psi. Listen for hissing and use soapy water to pinpoint bubbles. Do not exceed 20 psi to avoid damaging the intercooler. This is highly effective on the FA20DIT.
  4. Data log boost pressure: Use an AP (Accessport) or other tuning software to log actual vs. requested boost. A significant delta can indicate a leak or a restricted intake/exhaust.

Fixing Boost Leaks on the FA20DIT

Once you find the leak, the repair is usually straightforward.

  • Replace worn clamps with T-bolt clamps: When reinstalling piping, upgrade to constant-tension T-bolt clamps. They provide even pressure and are less likely to loosen over time.
  • Replace damaged hoses or intercooler: Use silicone hoses (e.g., Perrin or Grimmspeed) for long-term durability. If the intercooler is leaking, consider upgrading to a bar-and-plate unit (like a Process West Verticooler) that is more resistant to heat and pressure.
  • Replace throttle body gasket: Always use a new OEM gasket when reinstalling the throttle body. Torque to spec (around 8-10 ft-lbs).
  • Secure EVAP lines: Use zip ties or replace the rubber sections with a short piece of fuel-rated hose if they are cracked.
  • Check the wastegate: If the wastegate actuator diaphragm is torn, replace the entire actuator or the turbocharger if needed. A common upgrade on the FA20DIT is a 3-port boost control solenoid to better manage boost pressure.

External link for boost leak testing: Read more about GrimmSpeed's boost leak testing guide for a step-by-step walkthrough.

Preventative Measures to Keep Your FA20 Healthy

An ounce of prevention is worth a pound of cure, especially with the FA20's sensitive nature. Following these maintenance practices will minimize the risk of both oil consumption and boost leaks.

  • Use the correct oil and change it frequently: Subaru recommends 0W-20 for the FA20, but many experienced tuners move to 5W-30 for additional protection (especially under high load or track use). Change every 3,000-4,000 miles if you drive hard; every 5,000 for normal driving. Avoid extended intervals.
  • Install an AOS (Air Oil Separator) or catch can: A quality AOS (e.g., from IAG or Crawford) reduces oil vapor from the PCV system from recirculating into the intake. This dramatically reduces carbon buildup on intake valves and helps prevent oil ingestion that leads to consumption.
  • Regularly inspect and replace vacuum lines: The rubber lines in the engine bay harden over time. Replace them with silicone lines as a preventative measure. Pay attention to the lines connecting to the turbo and boost control solenoid.
  • Perform a boost leak test every 10,000 miles: Especially if you are tuned or race the car. Catching small leaks early prevents them from growing and causing drivability issues.
  • Keep the engine cool: Overheating accelerates ring wear and gasket failure. Use a high-quality coolant, ensure the radiator and cooling fans are in good shape, and consider an oil cooler for track use.
  • Avoid short-trip driving: Short trips prevent the engine from fully warming up, leading to fuel dilution in the oil and increased carbon buildup. If you drive short distances regularly, take the car for a longer drive weekly to burn off moisture and carbon.

When to Seek Professional Help

While many FA20 owners are handy with tools, some repairs require specialized knowledge. If you are unsure about any diagnostic step, or if you suspect internal engine damage (e.g., rod knock from oil starvation), consult a reputable Subaru performance shop. For severe oil consumption, a short block replacement by a trained professional may be more cost-effective than a backyard rebuild that fails prematurely.

For boost leaks, if you have access to a smoke machine, you can do it yourself. But if your car is heavily modified with aftermarket turbo parts, a dyno tuner or shop that specializes in the FA20DIT will have the expertise to identify and resolve leaks quickly.

Conclusion

The FA20 is a rewarding engine that, when properly maintained, delivers excellent performance and character. But it demands attention to its specific weaknesses, especially in the areas of oil consumption and boost leaks. By understanding the root causes – whether stuck piston rings, a clogged PCV valve, a cracked intercooler end tank, or loose charge pipe clamps – you can diagnose and fix these issues before they escalate into costly repairs. Regular maintenance, including frequent oil changes, an AOS, and periodic boost leak checks, will keep your FA20 running strong for many miles. Whether you daily drive a WRX or track a BRZ, staying proactive is the key to enjoying the full potential of this iconic boxer engine.