What is the biggest problem with Subaru engines?
Subaru's most persistent engine problem is head gasket failures in the older EJ-series 2.5-liter models, which can lead to coolant leaks, oil contamination, overheating, and costly repairs.
Subaru’s boxer (horizontally opposed) design and its long-running all-wheel-drive lineup helped build a reputation for durability, but certain generations carried a notable Achilles’ heel. The EJ-series 2.5L engines, used in popular models like the Impreza, Legacy, Outback, and Forester from the late 1990s through the early 2000s, became infamous for head gasket failures. In more recent years, Subaru introduced redesigned head gaskets and improved cooling passages in FA/FB engines, which mitigated many of these issues. Still, owners of older vehicles continue to face a higher probability of gasket-related repairs as mileage accrues.
The headline problem: head gasket failures
The following factors are commonly cited as contributors to head gasket failures in EJ-era 2.5L engines and similar setups.
- Aging multi-layer steel (MLS) head gaskets on the EJ25, which can weaken with heat cycles and time, leading to coolant leakage into the oil or combustion chamber.
- Cooling-system stress from overheating events or marginal cooling components (water pump, thermostat, radiator, hoses) that accelerates gasket deterioration.
- Head warp or crack caused by repeated overheating, which undermines the gasket seal and increases repair costs.
In summary, these factors collectively explain why EJ-series 2.5L head gasket failures have been a dominant reliability talking point for Subaru over the years, especially in high-mileage examples.
Symptoms and potential costs
Common signs include coolant consumption without an obvious leak, milky-looking oil on the dipstick, white exhaust smoke, overheating, and, in some cases, visible coolant/oil mixing at the tailpipe or inside the engine bay. Repair can range from gasket replacement to machining the heads and replacing the timing components, often making it a several-thousand-dollar job on an aging engine.
Other recurring concerns across Subaru engines
Beyond the head gasket issue, there are several other issues that owners frequently report across various Subaru engines, especially as vehicles age.
- Oil leaks from valve-cover gaskets, cam seals, and oil pans are a common maintenance item across many models.
- Oil consumption in certain engines and model years, particularly as engines accumulate high mileage, can lead to more frequent top-offs or more extensive repairs if not monitored.
- Non-turbo four-cylinders that use timing belts require regular belt and water-pump maintenance to avoid catastrophic engine damage if a belt fails.
- Turbocharged variants can experience turbocharger wear, oil feed issues, and related performance problems, especially on older units or those with high mileage.
- Coolant leaks from water pumps, hoses, and radiators, which, if ignored, can contribute to overheating and stress on engine seals.
Taken together, these issues underscore a common theme: Subaru engines often reward proactive maintenance and careful monitoring, particularly on older or high-mileage examples. Newer FA/FB engines have incorporated design improvements intended to reduce these failures, but vigilance remains important for legacy models.
Buying a used Subaru: what to check
If you’re considering a used Subaru, use the following checklist to screen for likely engine problems and to gauge the remaining lifespan of critical components.
- Inspect for milky oil on the dipstick or under the valve cover, which can indicate coolant mixing with oil from a failing head gasket.
- Check for signs of coolant leaks around the radiator, hoses, water pump, and by the back of the engine; look for sweet coolant smell or green/blue coolant residue.
- Look for white exhaust smoke, especially on startup or during acceleration, which can signal burning coolant or a gasket issue.
- Perform a compression or leak-down test to establish cylinder sealing and to detect head-gasket-related losses.
- Ask for service records showing head gasket inspections/replacements or cooling-system overhauls; verify timing belt service history if the vehicle has a belt-driven timing system.
- Visually inspect for oil leaks around the valve covers, oil pan, and cam seals; address any leaks promptly to avoid further damage.
With the above checks, a used Subaru buyer can better assess potential gasket problems, cooling-system reliability, and general engine health before making a purchase.
Summary
Subaru engines earn a strong reputation for durability, especially with proper maintenance. The single most notable risk over the years has been head gasket failures in the EJ-series 2.5L engines, a problem that has diminished in newer FA/FB designs but remains a consideration for older cars. In addition to gasket issues, oil leaks, oil consumption, timing-belt maintenance, turbocharger wear on forced-induction models, and cooling-system reliability are recurring themes across the lineup. For prospective buyers and owners, proactive maintenance, timely cooling-system service, and thorough pre-purchase inspections are the best defenses against costly engine problems.
