Subaru Head Gasket Woes: What Every Owner Needs to Know

The Truth About Subaru Head Gasket Failures and How to Fix Them

If you own a Subaru with the EJ25 engine, chances are you’ve either heard of or experienced the dreaded Subaru head gasket failure. It’s a well-documented issue that has left many owners frustrated, especially given Subaru’s lack of substantial support for the problem. I’ve worked on these engines, and I can tell you firsthand that replacing a Subaru head gasket isn’t just another routine repair—it requires precision, patience, and quality parts.

Why Do Subaru Head Gaskets Fail?

The EJ series engines have been around for decades, but the Subaru head gasket problem is particularly notorious in the EJ25 variant. These engines are found in some of Subaru’s most popular models, including the WRX, Outback, and Forester. Based on my experience and extensive research, most Subaru head gasket failures occur around the 100,000-mile mark, typically starting as a slow oil or coolant leak.

The culprits? Heat cycles and Poor Maintenance

Since Subaru engines are made of cast aluminum, they expand and contract as they heat up and cool down. This movement can wear away the coating on the original multi-layer steel (MLS) gaskets or damage older composite-style gaskets. In turbocharged models, increased cylinder pressure exacerbates the issue, especially when owners modify their engines to boost performance.

In addition, due to the design of the boxer engine, any coolant deterioration debris falls to the bottom of the engine, where it’s in constant contact with the head gasket. If you don’t change your coolant on time or don’t use the recommended coolant, the deteriorated coolant, debris, and acids can accelerate head gasket damage.

Diagnosing a Blown Subaru Head Gasket

If you suspect a Subaru head gasket issue, here’s what you need to do:

• Look for External Leaks: Oil or coolant seeping from the seam between the block and head is a major red flag.
• Check for Overheating: If your temperature gauge climbs higher than normal, especially under load, a failing gasket may be to blame.
• Perform a Combustion Gas Dye Test: This test detects exhaust gases in the cooling system—an almost certain sign of a blown head gasket.
• Inspect the Head Gasket Physically: In cases where overheating is severe, the gasket may be visibly burned through the fire ring upon removal.

Should You Remove the Engine to Replace the Head Gasket?

Subaru’s official service manual states that you don’t need to remove the engine to replace a Subaru head gasket, even for double overhead camshaft (DOHC) models. That said, many experienced technicians—including myself—prefer to pull the engine. Why? Because it allows for a more thorough repair. With the engine out, you can properly clean and inspect the deck sealing surfaces, check for cracks, and even replace the rear main seal and other wear-prone components.

If you’re tackling this job yourself, it involves removing most of the intake and accessory components. Sending the heads to a machine shop to be milled flat is crucial—skipping this step is a surefire way to have the problem return prematurely.

Upgrading to a Better Head Gasket

There’s a lot of disagreement on which gasket to use. Some engine rebuilders swear by the OE gaskets, while others prefer aftermarket gasket sets. Some gasket makers offer a premium aftermarket gasket with improved coatings and reinforced cylinder armor. These upgraded gaskets are designed to handle the repeated heat cycles that cause failure in the first place.

Also, don’t reuse the old head bolts. Many Subaru engines use torque-to-yield bolts, which stretch during installation. Reusing them can lead to improper torque and gasket failure down the line. Even if the bolts in your engine aren’t TTY, keep in mind that this is a big job, and you only want to do it once. Why risk the job by reusing old head bolts?

What Else Should You Replace?

A Subaru head gasket job isn’t just about the gaskets. While you’re in there, consider replacing:

• Timing belt, tensioner, idlers, and cog wheel. Those parts are rated for the life of the belt. If the engine is already at the 100K mile mark, you’re playing with fire by reusing these parts. A single failure can destroy the engine.

This is an example of what happens when you reuse old parts when performing a Subaru head gasket replacement. The shop that did this casket reused the old idlers and cogwheel. The cogwheel bearing failed, and the engine was destroyed.

• Water pump and idler pulleys— The old engine had at least 100K miles on it, and there’s no way the old water pump is going to last another 100K miles. The last thing you need after doing all this work is to wind up with a leaking water pump in the next 25K miles.
Drive belt (especially if it’s a stretch-fit A/C belt)
Belt tensioner (if the vehicle has more than 100,000 miles)

OE or Aftermarket Components

Many drive belt manufacturers sell idlers and tensioners. But they don’t manufacture those parts; they buy them from 3rd party suppliers. Before you buy any tensioners or idlers from eBay or Amazon, think about how much is at stake here. This is a $3,000 job if you had a shop do the work. Would you want them to install aftermarket parts of unknown quality? Well, the same applies here. You’re saving money by doing the work yourself. Don’t be a cheapskate by buying cheap parts. When it comes to these critical parts, I always buy OE.

Final Thoughts

By the time most Subaru head gasket failures occur, the factory warranty is long gone. Subaru only covers head gaskets under the 3-year/36,000-mile factory warranty or the 5-year/60,000-mile powertrain warranty. If you’re buying a used Subaru with an EJ25 engine, check the service history carefully. If the gaskets haven’t been replaced, budget for the repair—it’s almost inevitable.

Replacing a Subaru head gasket the right way isn’t cheap, but if done properly with the right parts and techniques, you won’t have to worry about the issue again. If you own an EJ25-powered Subaru, take proactive steps to catch leaks early, maintain your cooling system, and, if needed, tackle the repair with confidence.

©, 2025 Rick Muscoplat