Subaru Boxer Engine Problems: 5 Issues Owners Report | SlashGear

Subaru’s boxer engine is a defining characteristic of the brand, but it hasn’t been without its issues. While Subaru consistently ranks well in reliability studies – second most reliable according to Consumer Reports’ 2024 findings, trailing only Toyota – the 2025 J.D. Power Vehicle Dependability Study places them 17th, a slight dip from their 15th place ranking in 2024. Despite this, the boxer engine remains central to the Subaru experience and certain problems have become well-known among owners. Here are five common issues reported with Subaru boxer engines, and what owners should know.

Head Gasket Failures

Perhaps the most infamous problem associated with Subaru boxer engines is head gasket failure. Starting in the early 2000s, this issue became so prevalent it almost became a running joke. The problem most commonly affected 1990s Impreza, Outback, and Legacy models, though reports continue to surface with newer vehicles. Impact Auto Repair lists head gasket problems as the most frequent repair they encounter on Subaru vehicles.

Online forums, like Reddit’s r/cars, show a mix of resigned humor and genuine concern from owners. While many early reports focused on 2.5L engines from the early 2000s, even owners of newer models, like a 2021 Impreza, have reported failures. A 2014 Forester owner on the Subaru Forester forums was quoted $3,500 for a repair.

Subaru repair specialist MrSubaru1387 explains the root cause as a breakdown of the graphite coating within the head gasket due to heat cycles and age, exacerbated by neglected coolant maintenance. He notes that repeated failures are not uncommon, suggesting this isn’t always a one-time fix.

Oil Leaks

While head gasket failures have become less frequent in modern Subaru engines, oil leaks remain a common complaint, particularly with FA and FB engines. These leaks often originate from the cam carriers and timing chain covers. The issue stems from the degradation of the RTV silicone sealant used in these engines, creating gaps that allow oil to seep through.

A technician from MRT Performance explains that the sealant simply doesn’t hold up over time. Because the camshaft is no longer integrated into the cylinder head (as in older EJ engines), this creates another potential sealing surface prone to leaks. Reddit users report that repairs can be labor-intensive, potentially costing around $3,000 at a dealership due to the extensive disassembly required – removing the engine, timing chains, and then resealing the cam carriers.

Subaru acknowledged this issue with Service Bulletin 02-131-12R, providing detailed procedures for inspecting, resealing, and replacing o-rings, and sealant.

Timing Issues

Timing chains, designed to last the life of the engine, can sometimes stretch or experience tensioner issues in Subaru’s newer FA and FB engines. This can result in rattling or slapping noises, especially during cold starts. Owners on the Subaru Forester forums report a brief metallic rattle at startup or low speeds.

Older EJ-series engines used timing belts, which are even more prone to failure. MrSubaru1387 points to tensioners and idler pulleys as the most common culprits, rather than the belt itself. Subaru Clinic recommends replacing the timing belt every 105,000 miles. Because Subaru’s EJ engines are “interference” engines, a broken belt can cause the valves and pistons to collide, potentially requiring a complete engine replacement.

One Reddit user in the r/subaruimpreza forum noted a near 100% chance of piston-to-valve contact if the belt breaks. Preventative maintenance, avoiding overheating, and regular inspection of the belt, tensioner, idler pulleys, and water pump are crucial.

Oil Consumption Issues

Excessive oil consumption is another frequently reported problem, particularly in models between 2011 and 2015 (Forester, Legacy, Outback, Impreza, and XV Crosstrek) equipped with 2.0L or 2.5L FB engines. This issue was significant enough to trigger a class action lawsuit against Subaru, resulting in extended warranties, reimbursements, and free repairs for over 665,730 vehicle owners.

Subaru issued Technical Service Bulletin 02-157-14R, extending the powertrain warranty to 8 years/100,000 miles for affected vehicles and outlining inspection and repair procedures, including engine short block replacement. The root causes are often linked to piston rings, low ring tension, valve guide issues, PVC leaks, or turbocharger leaks.

While newer models appear less susceptible, owners on the Subaru Forester forums suggest the problem is most pronounced in early FB-series engines.

Spark Plug Fouling

Oil seepage into the spark plug tubes is a known issue in certain Subaru boxer engines, caused by aging valve cover gaskets and spark plug tube seals. This oil can foul the ignition coil boots, leading to misfires and performance problems. RepairPal reports that over 109 different Subaru owners have reported this issue.

All Wheel Drive Auto Independent Subaru Expert explains that the tube seals, initially rubber, can harden over time and lose their ability to expand with the valve cover as it warms up, allowing oil to leak. Replacing the valve cover gaskets and tube seals is the recommended solution. A fouled spark plug will typically appear black and sooty, and may cause rough idling or difficulty starting the engine.

Accessing the spark plugs in Subaru boxer engines can be challenging due to their 180-degree layout.

How We Made Our List

Our research involved consulting a variety of sources, including independent Subaru mechanics and performance specialists on YouTube, reports from Subaru owners on forums like Reddit and brand-specific Subaru forums, Subaru’s own technical service bulletins, and resources like Impact Auto Repair and RepairPal.

We prioritized issues consistently reported by multiple owners, cross-referencing them with expert insights to understand the underlying causes and recommended fixes. We aimed to provide a balanced view, incorporating both anecdotal evidence and professional assessments. While individual experiences may vary, these represent the most commonly reported problems with Subaru boxer engines.