subaru Outback problems

There’s a stain on every Subaru independent’s shop floor in the same shape — a crusty yellow trail under the engine cradle, drying coolant from the EJ25 head gasket that came in last week and the one before it and the one before that.

Subaru spent the last 25 years building one of the most loyal owner bases in the business. Subaru drivers don’t buy Subarus. They commit to Subarus. That kind of brand loyalty is exactly what allowed the company to ship the EJ25 head gasket problem for the better part of two decades without ever admitting it was a design flaw.

If you own a 1999-2009 Outback, Forester, Legacy, Impreza, or Baja with the 2.5L SOHC EJ25 engine — and a fair number of 2010-2012 cars too — head gaskets are not a question of if. They’re a question of when, how bad, and what you’re going to do about it.

Why they fail

The EJ25 is a flat-four (boxer) engine. Two cylinders pointing left, two pointing right, crankshaft horizontal in the middle. The head gaskets sit on the side of the block, not the top, which means coolant passages cross the gasket vertically. Subaru spec’d a multi-layer steel (MLS) gasket on later years and a graphite-composite gasket on earlier years, neither of which held up to the thermal cycling of the boxer architecture combined with marginal coolant flow at the rear cylinders.

The failure mode on most EJs is external — coolant weeps out the side of the block where the gasket meets the head. You find a small puddle in the driveway or smell coolant on a long drive, and over months it gets worse. Less commonly, it fails internally and you get coolant in oil or oil in coolant, which is a different and uglier conversation.

The 1996-1998 DOHC EJ25 had a different and worse failure mode. The 2006-plus revised gasket on the SOHC EJ25 is somewhat better. The EJ25 turbo versions (WRX/STI) have their own gasket problems related to detonation.

What you’ll see and hear

• Sweet smell from the engine bay, especially after a hard drive
• Coolant level in the overflow tank slowly dropping — half an inch every 1,000-2,000 miles
• Crusty white-yellow residue on the side of the block, usually visible on the left bank near the rear of the engine
• Small puddle of coolant on the ground after a hot-shutdown, sometimes on the passenger side under the engine
• Overheating — late stage, after the leak has progressed to where the system can’t maintain pressure
• Bubbles in the radiator or overflow when running — combustion gas getting into coolant, internal leak, time to stop driving it

A small external leak is annoying but not immediately dangerous. A car that’s overheated is a car where you may have already warped the head and made a $2,000 job into a $4,000 one.

What to do about it

There’s a real choice here, and Subaru owners argue about it endlessly:

Option 1: Fix it right when it shows up. Pull both heads, resurface them (it’s machine shop time, $150 a pair), install OEM 6-layer MLS gaskets (the revised “Six-Star” Subaru gasket — part number changed somewhere around 2009), new head bolts, fresh thermostat, new water pump while you’re in there, new timing belt and pulleys if it’s an interference engine year (most are). Cost: $1,800-$3,000 at a Subaru independent shop, $3,500-$5,000 at a dealer. Done right, it’s a one-and-done.

Option 2: Use a chemical sealer. Subaru actually sells a coolant conditioner (part number SOA868V9270) that some dealers add to the coolant on suspected weeping cars. Independent shops use Bar’s Leaks or similar. It works on small external weeps, sometimes for years. It does nothing for an internal leak. Cost: $15 plus a coolant flush. It’s a band-aid. On a high-mileage car you’re going to sell in two years, fine. On a car you’re keeping, do the head gaskets.

Option 3: Drive it till it stops. Top off coolant weekly, drive carefully, watch for overheating, plan to replace the engine when it finally fails. Free until it isn’t. I don’t recommend this but I’ve seen people get 50,000 miles out of a leaking gasket by being patient about it.

Should you buy one?

Yes, with caveats. The Subaru drivetrain is otherwise excellent — the AWD system is genuinely good, the chassis is durable, the platform handles snow and rough roads better than just about anything in its class. If you’re shopping a used Outback or Forester:

• 2000-2005: assume head gaskets need to be done if not already documented. Negotiate $2,000-$3,000 off the asking price.
• 2006-2009: assume gaskets will need to be done before 200,000 miles. The revised gasket helped but didn’t solve.
• 2010-2012: better, but still not bulletproof. Maintenance records matter.
• 2013-plus: switched to FB25 engine, a different design, much better head gasket durability.

If you already own one and the gaskets are holding: change coolant every 30,000 miles with the OEM Subaru long-life (the blue stuff), check the level monthly, and budget for the gasket job somewhere between 150,000 and 250,000. It’s not the end of the world. It’s the price of admission to a Subaru.

The EJ25 is otherwise a stout little engine. Boxer rumble, low center of gravity, easy to work on once you’re past the head gasket problem. Subaru owners aren’t crazy for loving these cars. They’re just also right that the head gaskets are real.