Subaru Flat-Six Engine Teardown Shows No Damage at 200,000 Miles

When it comes to Subaru engines, attention generally falls to the boxer four. And why not? From the old EJ22T to the EJ25 that powered pretty much every Subaru at one point, it’s the engine that’s synonymous with the Japanese brand.

That’s what makes this I Do Cars video so interesting. It focuses on the lesser-known 3.0-liter EZ30 flat-six, pulled from a 2005 Subaru Outback that had just over 200,000 miles. We’re used to seeing complete carnage from these teardown videos, and this engine was deemed too faulty to save. But the diagnosis was the result of a failed leakdown test, and upon inspection, it’s not immediately clear what might’ve happened.

What is clear, however, is that this engine has been out of a car for quite some time. Significant corrosion around the outside is visible right from the beginning, and that makes this teardown infinitely more difficult. Stubborn bolts end up breaking, and damage isn’t relegated to fasteners. While taking one of the valve covers off, a corroded bolt actually breaks the cover. The rest of the cover is literally broken into pieces while trying to remove other stubborn bolts. Subaru’s H6 may have a reputation for reliability, but it sure doesn’t like coming apart.

But the disassembly process continues, and with each part removed, its reason for being condemned becomes a bigger mystery. Finally we get to the bottom end where, usually, we see some form of mutilated metal. But not this time. Aside from some abnormal (but not detrimental) wear on the rod and main bearings, everything in this engine is fine.

So what gives? This engine initially failed a leakdown test, suggesting a loss of compression in a cylinder. That usually means significant damage to some internal components, but in this case, it may have just been some corrosion in the valvetrain preventing valves from sealing properly. It’s even theorized that, after running and reaching operating temperature, the engine may have basically fixed itself. Now, that will never happen.

But the video shows the inner workings of a seldom-seen Subaru engine, and to the automaker’s credit, it looks pretty overbuilt. At the very least, engineers sure made it difficult to take apart. Keep that in mind the next time you decide to postpone an oil change on your flat-six Subie. If anything does happen inside the engine, even something minor, it’s going to be a major expense getting it fixed.