4 Common Subaru Head Gasket Problems (Symptoms and Fixes)

Subaru is world renowned for creating sweet-sounding, turbocharged engines. Who doesn’t love a JDM powerplant that goes “STU TU TU”? But, there is one thing that Subaru engines are known for – unreliability!

If you are a fan of Subarus, this article is for you! Today, we will tell you everything you need to know about one of the most common reliability issues affecting various Subaru models – head gasket failure. In addition, we’ll take a look at the common causes, symptoms, and fixes for this notorious problem.

Manufacturing defects, overheating, and pre-ignition inside the combustion chamber are some of the most common reasons for Subaru head gasket failure. Remember to check for these issues before purchasing your next Subaru.

The main responsibility of the head gasket in an internal combustion engine is keeping the combustion chamber sealed. Not only does this allow the engine to maintain compression, but it also prevents oil and coolant leaks.

Modern Subaru engines use metal-shim style (MLS) head gaskets. These are made by riveting layers of thin steel together and also come with a sealing coating. Although modern construction techniques have made head gaskets more durable than ever, head gasket failures still remain a common complaint of Subaru owners.

Let’s start things off by taking a look at the common symptoms of Subaru head gasket failure.

Symptoms of Subaru Head Gasket Failure

Subaru Head Gaskets - What You Need To Know - STechnic

Here, we have listed some of the most common giveaways of a blown Subaru head gasket.

  1. White smoke from the exhaust
  2. Low coolant levels
  3. Blue exhaust smoke
  4. Loss of engine power
  5. Bubbling in the radiator
  6. Engine oil contamination
  7. Rough running engine

White smoke from the exhaust

Excessive white smoke accompanied by a sweet smell coming from the tailpipes of your Subaru is a tell-tale sign of head gasket failure. But, what causes the white smoke in the first place?

When the head gasket fails, it leaks coolant into the combustion chamber. As you might already know, coolant contains water, which gives off steam when it reacts with heat. The steam then comes out of the tailpipe, appearing as white smoke.

Low coolant levels

If you notice your Subaru’s coolant levels running low constantly, a blown head gasket might be the one to blame. You see, the head gasket is responsible for separating the combustion and cooling systems. When it blows, the coolant will escape into the engine block, causing the reservoir to run low.

Insufficient coolant levels can cause a whole host of issues, which we will discuss later on in this article. So, it is essential that you keep an eye on the coolant levels if you want to avoid expensive repair bills.

Blue exhaust smoke

Similar to white smoke, blue smoke is also indicative of head gasket problems. The distinctive blue color stems from the burning of lubricating oils, which have made their way to the exhaust system through a blown engine head. Additionally, engines that are burning oil excessively also produce blue exhaust smoke.

Loss of engine power

If you are experiencing intermittent power loss, there is a high chance that your Subaru is suffering from a head gasket problem. Adequate engine compression is essential for optimal performance. A blown head gasket allows compression to escape, reducing engine performance in the process.

Bubbling in the radiator

Exhaust gases leaking from a blown head gasket can cause bubbles to form in the radiator even when the engine is running cold.

Engine oil contamination

Milky residue in the engine oil is one of the most prominent indications of a blown head gasket. This contaminant forms when the oil inside the engine mixes with the coolant that has escaped through the damaged head gasket.

Over time this thick, milky-brown froth collects under the engine oil filler cap and on the dipstick. If you suspect that your Subaru is suffering from a head gasket problem, now you know where to look!

In addition to looking disgusting, contaminated engine oil causes catastrophic damage to your Subaru engine’s internal. In addition to replacing the head gasket, engine bearings, and oil filter, you’ll have to perform a complete engine flush too.

Rough running engine

When coolant escapes through the head gasket, it interferes with the combustion process. Additionally, head gasket issues make the engine lose compression. These problems lead to several engine issues, including misfires, engine knocks, and rough idling. If these engine problems appear out of the blue, we recommend taking your Subaru to a mechanic as soon as possible.

Now that you know some of the main symptoms of a blown Subaru head gasket, let us look into what causes this to happen in the first place.

Most Common Causes of Subaru Head Gasket Failure

Subaru Head Gasket Problems

Apart from the weakness in construction we mentioned earlier, there are a number of other reasons that can cause your Subaru’s head gasket to fail.

  1. Overheating
  2. Pre-ignition
  3. Poor cylinder reinforcement
  4. Cylinder wall thickness


Overheating is one of the major reasons behind head gasket failure. Coolant leaks, problems with the cooling system, and over-revving the engine before it warms up can all result in an overheating engine.

All of these situations put the head gasket under extreme stress, leading to the formation of cracks and leaks.


When talking about Subaru head gasket failures, we can’t ignore talking about pre-ignition. Pre-ignition refers to when combustion occurs prematurely, resulting in pressure buildup inside the cylinder head.

Over time, these rapid pressure differences can wear out and strain the head gasket to breaking point.

Poor cylinder reinforcement

Some Subaru engines didn’t come with enough reinforcement around the cylinders, thanks in part to their “open deck” design. As the engines continued to run, the lack of reinforcement caused the cylinder sleeves to flex ever so slightly, especially at high RPMs.

As time passes, repeated flexing wears out the head gasket, weakening the seal between itself and the engine block. Luckily, this issue doesn’t affect Subaru engines that have “closed deck” and “semi-closed deck” designs.

Cylinder wall thickness

Out of all Subaru engines, early EJ25s produced from 1996 to 1999 are the most notorious for blowing their head gaskets at an alarming rate. The bore size of these powerplants increased from 96.9mm to 99.5mm from the previous generation.

Although this increased engine performance, this had the adverse effect of weakening the cylinder walls. The thinner cylinder walls were another contributing factor to the head gasket issues that plagues Subarus.

Preventive Maintenance Tips To Limit Subaru Head Gasket Problems

If you already own a Subaru and are worried about the head gasket going “KABOOM!” here are some preventive tips you should follow.

Replacing coolant on schedule

Ideally, you should flush out the coolant in your Subaru every 24,000 – 36,000 miles. Otherwise, the fluid will become corrosive and damage the head gasket. Additionally, it will ruin the seals in the cooling system as well.

Make it a regular habit to check the coolant levels, and remember to top off the reservoir if the levels have gotten low. Pay attention to the color of the fluid as well. Fresh coolant fluid has a bright red, green, yellow, or orange hue. If it is a darker shade, it is time for a coolant replacement.

Look after the battery

Car batteries are prone to corroding, especially if you don’t look after them properly. But, how does battery corrosion tie into head gasket problems? Let us explain.

A corroded battery gives out acids, which can get vented out through the cooling fans. If these acids come into contact with the metal gaskets, you’re in some deep trouble.

The chemical reaction between the head gasket and battery acids will corrode the head gasket, weakening it in the process. We recommend keeping an eye on the condition of the battery and replacing it every 3 to 5 years to minimize the possibility of this happening in your Subaru.

Change engine oil regularly

Regular engine oil changes are the final and most important step you should follow in order to prevent head gasket issues. Contrary to popular belief, an internal combustion engine does not burn all the fuel that makes its way into the combustion chamber.

Some of the fuel remains unburnt, and it can make its way through the crankcase and mix with the engine oil. Although most of this excess fuel evaporates when the engine oil gets hot, some will remain mixed with the lubricant.

Over time, this fuel dilutes the engine oil, limiting its capabilities. Not only that, this fuel damages the head gasket and other seals as well. So, it is important that you swap out the engine oil on schedule. Subaru suggests owners perform engine oil changes every 6000 miles or six months.

The worry about head gasket issues deters most gearheads from purchasing Subarus. Luckily, most recent engines from the manufacturer have remedied these problems. By following our tips and keeping an eye out for the symptoms we discussed, you can easily prevent head gasket problems and enjoy the driving pleasure of a Subaru to the maximum.

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4 Common Problems With Subaru Boxer Engine


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