Subaru Head Gaskets Explained part II

In this article I am going to cover the current trends with the Subaru Head gasket problem focusing only on the phase 2 2.5l SOHC from 1999 to 2011 in the  Forester and 2000 to 2009 in the Legacy, Outback and Impreza with an emphasis on the 2005 and newer models.  This article is going to be fairly long as there really is a lot of information that I want to share.  I had thought about breaking it up into two smaller articles but realized that the one read without the other would leave to many questions unanswered so please take the time to read the article in its entirety and hopefully you will have learned a little more about your Subaru. If you have not yet had a chance to read the first article and the over 1000 posts for Subaru Owners around the Globe you can do so here

If you are taking the time to read this then you most likely are doing a little research before you buy a used Subaru or you already own a Subaru of this era and have either recently been told you have a head gasket leak or are just taking the time to learn a little about the car you own.

Head gaskets in a phase two 2.5l can leak in three very different ways.

The first is an external coolant leak typically from the driver’s or left side head gasket, this affected the pre 2003 models specifically and ultimately led to the WWP-99 campaign where Subaru added a “coolant conditioner” otherwise known as stop leak and extended the warranty period to 8 years or 100k for external coolant leaks only. This is found doing a visual inspection of the bottom side of the engine for fluid leaks, which should be done every oil change by a qualified Technician who does not work at a lube center.

The second type of leak is an external oil leak and while it’s true that any car can and will develop an external oil leak from the head gasket, the design of the horizontal engine platform lends itself to a situation where the smallest of oil leaks is immediately apparent  in the form of a drip. This is found while performing a visual inspection of the bottom side of the engine for fluid leaks, which should be done every oil change by a qualified Technician who still does not work at a lube center.

I want to stress that just because you have not yet seen fluid in your driveway does not mean you do not  have a fluid leak from a head gasket.  Subaru models have a splash pan with a fibrous pad (that I call a diaper), this must be removed to inspect for leaks.  The pad also does an incredible job of soaking up oil and coolant.

The third and final type of a head gasket leak on a phase two 2.5l is an internal failure of the gasket resulting in a breach between the combustion chamber and the cooling system which will ultimately cause the vehicle to overheat and is often misdiagnosed by many at the early stages which can increase the likelihood of future problems such as high oil consumption after repairs.

You may have already seen some pictures like the ones below highlighting where the gasket material has been eaten away.

Phase 2 Subaru 2.5l SOHC Head Gasket

Subaru 2.5l Phase Two Head Gasket

Gaskets that have had this much head gasket material  deteriorate away most likely leaked  fluid for a while before finally being replaced which is fairly typical.  Generally speaking it is an acceptable practice of our shop to monitor minor oil leaks for our customers and advise them as they become worse or begin to leak coolant.  I will tell you that for some customers we have been monitoring oil leaks for 5 years or longer and others have had the repairs done a few oil changes after first being informed about the situation.  Why I really like this way of dealing with the external fluid leaks is it gives the driver a bit of time to either budget for the repairs, if the car still suits their needs,  or come up with a plan to move on if the Subaru no longer fits the family.  If you really think it through to conclusion its not too often that you actually are awarded the opportunity to make a big decision over time, many times an expensive repair like this happens as quickly;  such as a transmission failure or broken timing belt giving you no notice and even less time to budget for the repair.

When a head gasket fails like this one below the situation can be much more dire.

Internal Failure of Aftermarket Subaru Head Gasket

This head gasket has had a breach in between the cooling system and the combustion chamber allowing  both pressure and temperature from the combustion chamber into the cooling system.  There are two very distinctive issues that happen with this type of failure.  The cooling system can only handle so much pressure in fact in terms of cooling system pressure the radiator cap will allow coolant to flow into the cooling system overflow bottle at pressures around 15 psi. depending on which model of Subaru you have. Now imagine 175 lbs. of pressure coming into the cooling system from the combustion chamber.   Next the increased pressure thats coming into the cooling system is also very hot as combustion temperatures can vary but will typically be well over 500 degrees Fahrenheit, and there isn’t a coolant temperature gauge ever put into a production vehicle that will read that kind of temperature.  This further increases the pressure in the cooling system as the higher the temperature the higher the pressure.  This increase in temperature and pressure is something the cooling system just can’t contend with. What happens next is the coolant in the radiator is pushed into the overflow bottle to the point that the overflow tank is now full and begins to spill coolant out of the tank and onto the ground until finally the engines cooling system is low and the engine overheats.  As I have mentioned before in the first article and I am still amazed and even years and years later this very simple fact seems to escape so many technicians across our nation. I have had to often wonder if either they have had no real education, or just lack the ability to truly understand the internal combustion engine.  We have replaced Honda, Toyota and Nissan Head Gaskets at our shop as well and have looked for internal failures the same way as we do for the Subaru.

Testing for internal failures is not a difficult task but I have responded to well over a thousand replies in the first head gasket article, many start out with the same story, the Subaru began to run hot but didn’t overheat, then it overheated, then a shop replaced the thermostat, then the radiator, then the cooling fans, then the kitchen sink, then threw in the towel.

Below is another head gasket with a breach in the gasket area between the cooling system and the combustion chamber.

Please look at it closely, and picture what I am about to explain.

Internal Failure of Head Gasket on a Subaru 2.5l

When the engine is cold the breach does not affect the seal of the gasket as much and may actually still seal when the cooling system is pressure checked at 15 to 20 lbs. of pressure when the engine is cool.  Doing a compression test on a relatively cool to warm engine may also not reveal any issue.  Performing a leak down test may show a percentage of leakage, but almost always 10 to 20% to the  crankcase as again until the engine is at normal operating temperature the piston rings are not fully expanded into the cylinder walls improving the “seal”.

The smaller the breach such as in this picture, the less likely you will find it with any of the above test procedures.

Internal Failure of Subaru Head Gaskets

What must be done instead to find the smallest of internal leaks at an early and manageable stage is to look for the presence of combustion chamber gases also known as exhaust in the cooling system.  The single easiest exhaust gas to identify is HC or hydrocarbon emissions but this needs to be done one and one way only and thats with an exhaust gas analyzer in good working order!   You must run the Subaru hard and get it up to operating temperature before looking for this failure as it may not show up just idling along under no load and with less combustion events  happening.

Looking for Failed Subaru Head Gaskets

Testing For Internal Failure of the Head Gaskets

You see as I mentioned at the beginning  that testing cold would yield different results than testing when hot. Temperature causes expansion, expansion of the cylinder head away from the engine block, expansion of the gasket away from the block, and now that breach in the gasket becomes a bigger issue.  Compound that with the combustion events happening in the combustion chamber at higher RPMS meaning there are more of them!  The relentless pressure put to the weakened head gasket is more than it can contend with.  Now that the engine is running at the extremes which is coincidentally almost always the same way it over heats for the driver but seldom the way that many attempt to test for failures.  If you have an overheating situation in your Subaru and it has not been tested, exactly as I have presented above; and the shop is still stumped; the reason for that is it has not been tested!  Its not feasible to do a compression or leak-down test on an engine that is hot, as you will burn your self or damage the spark plug threads removing the plug and inserting the tools.

I have now covered the three different ways a head gasket can fail.  Let’s now focus on prevention.  As you have seen in the pictures above the gasket material was eaten away, this happens in a few different ways and you really need to understand what you own and take care of it accordingly.  The horizontally opposed engine has many benefits which is why Subaru has stuck with it and Toyota has also looked to Subaru for an engine for a sports car.  I won’t list all of the marketing points behind the boxer here, but please do your own research and understand how it enables a capable, safe, AWD platform  unmatched at its price point.

The single biggest back to a boxer engine is that the critical engine fluids such as coolant and oil will remain in contact with the gaskets as opposed to an Inline or V engine the fluids drain down or only contact the side of a gasket rather than gravity forcing it to stay on top.  This is where Subaru has kind of gotten themselves in trouble in my opinion as the maintenance aspects of a Boxer need to be different than that of an inline 4 cylinder engine for example.  If the oil is contaminated with fuel, and the coolant ph levels increased the gaskets will be eaten away, they don’t have a choice.  The single most important thing you can do with your Subaru is change the oil and change the coolant the way YOUR driving style dictates, how you use the car is what matters not some hard to understand fiction put into a maintenance booklet so the ownership costs look lower than they actually are.

Other aspects of maintenance that are important are the types of components used such as the thermostat.  Pictured below is a O.E. Subaru thermostat VS an aftermarket thermostat made by a chinese parts company and sold to you at every local parts store under the claim “meets or exceeds” .

Subaru Thermostat VS Aftermarket

This is just one example of many but the one I point to most often since a picture is worth a thousand words, and just about anyone looking at the 2 different parts here would understand one is inferior. We have seen on many occasions the thermostat on the right cause damage to head gaskets. Make sure if you or a general repair shop is replacing the thermostat that a Subaru thermostat and only a Subaru thermostat is installed.

The next thing I want to bring up is the fuel octane requirements here in the U.S.,  which has nothing to do with Subaru, but Subaru must make vehicles that will run on lower fuel ratings here in the U.S. then anywhere else in the world.  Octane is about controlling knock from explosions, many think that explosions are desired and I find my self using that term as a good way of explaining why gaskets fail internally, but we are really after a “prolonged burn” and no explosion.  The higher the octane number the better chance you wont have an explosion in the combustion chamber. The less explosions the better the chance the head gaskets will survive what happens in the combustion chamber.  Subaru has built engines that require premium and some have been hard to sell for that reason. In our country you will find it hard to sell a 4 cylinder vehicle with the fuel economy drag of AWD and then require more expensive fuel unless it has the fun factor of a Turbo and thats a different demographic than just a 4 cylinder Outback driver.  Which is one of the reasons most of the head gasket issues are about the U.S. cars NA (naturally aspirated), not the European and JDM( Japanese Domestic Market) models.  If you want to try avoid the whole head gasket thing consider using premium fuel. Next if you ignore a check engine light with a P0325, 0r P0328 set pertaining to a knock sensor  or circuit you are also potentially inviting future head gasket failure as there is no longer any precision happening, instead the computer may be running on fixed programed values rather than real time changes based on live data from the knock sensor.

2005 and newer models?

I answer this question a lot.  Didn’t Subaru fix that head gasket issue?

The answer is yes and no!  The gasket used in the 2003 and newer models is more resistant to corrosion.  Subaru has insisted on the use of Genuine Subaru coolant and the use of the cooling system conditioner and has increased the number of ground straps on the later model cars, all of these factors have resulted in a huge decline in potential and actual failure of the head gasket resulting in an external coolant leak.  We rarely see elevated PH levels on the late model Subaru’s cooling systems when serviced regularly now.  Whether this was an intent of the increased number of ground straps or not it has been a positive result.

Subaru Coolant and Conditioner

Ground Straps?

This next thing is always a challenge to explain, and is really nothing new to cars but has been lost by so many.

The cooling system acts as a ground as you can see in this picture below.  The positive probe is connected to the positive terminal, the negative terminal inserted into the radiator.  What I am showing you here is that the flow of electrons is also through the cooling system.  The test for Voltage  and PH levels in the cooling system is different than this one.  If you have ever owned a hot-tub or a swimming pool you know the importance of maintaining proper chemistry in the water, the same is true of your cooling system.  Over time the flow of electrons in the cooling system affects the chemistry in the cooling system and must be addressed as this occurs.

Voltage in the cooling system

Subaru Ground Strap

Subaru Ground Strap

The increased number of ground straps is one contributing factor to how Subaru was able to decrease the likely hood of failure of one spot of the head gasket due to corrosion in the cooling system attacking one location adjacent to the main ground cable, which is why the left side cylinder head gasket is typically the one that leaks coolant externally in the early phase 2 2.5l.  By improving the entire primary circuit in the car all of the systems function better as a result.

Why is this important?

In the picture below is an extreme case of corrosion, but one we see all to often, its not what you can see here that causes concern its what you cant see until you cut into the battery cable and see how far up the cable this is, or test for the presence of voltage in the cooling system as well as elevated Ph levels. This increases the “on time” of the alternator which is ultimately the cause of the contamination in the cooling system.  Just like copper will patina over time in the elements, it takes time for corrosion to form, and time for the corrosion to do its damage.  Not letting the below happen will help ensure you are not stranded for a primary circuit related failure, such as a dead battery or corroded in half battery cable, but it will also prolong the overall longevity of all other related system in the car. Baking soda and water was something EVERYONE used to do to their battery and terminals, now not so much and this is something that anyone can do.

Corroded Battery Cables

We really don’t see the same type of external coolant leaks from the phase two 2.5l anymore as a result of a combination of factors as I have tried to explain above.  However we still see oil leaks, and the oil leaks can eventually lead to coolant leaks but generally at much higher mileage.

One of the common trends  in the 2005 and newer models are warped heads, the majority of the head gasket repairs we make on the 2005 and newer models require that the cylinder heads in fact be resurfaced.  This is due to a couple of different factors, first and foremost Toyota worked with Subaru to increase the economy of the engine and in doing so the combustion chamber area of the cylinder head was enlarged resulting in less surface material making the cylinder head more prone to warping.  The second is that the primary catalytic converter was moved closer to the engine to increase efficiency, but this also brought the intense heat and weight of the Catalytic convertor closer to the cylinder heads allowing for the greater possibility of warp from heat and the weight of the exhaust system so close to the Cylinder heads. I do want to stress that many of the repairs on the 2005 and later models is due to external oil leaks with a small percentage of those repairs also leaking coolant, and a smaller number with internal failures as well.

Please note in the pictures below that the the Catalytic convertor now sits just below the cylinder heads

2005 & Newer Subaru Catalytic Convertor Location

2005 & Newer Subaru Catalytic Convertor Location

Please note the difference in the combustion chamber area of the cylinder heads side by side in the picture below. 2005 and newer Subaru 2.5l NA have a larger combustion chamber which results in less cylinder head surface area.

Subaru Cylinder Head Comparison

You can clearly see the difference in the two different era of cylinder heads; the one on the right for your reference is from a 2006 Outback, and the one on the left from a 2001 Outback, both with a 2.5l NA SOHC or phase 2 2.5l. It was fairly uncommon to need to resurface the heads prior to this change unless it over heated, leaked coolant excessively or the head surface couldn’t be cleaned by block sanding alone.   I am not sure how many independent Shops are actually aware of the current trend and I want to stress that “a repair” is not necessarily better than “no repair”.  I really don’t want to damage any relationship you may have formed with the current service provider  if you need to have this repair made, but I also want to stress that I don’t believe it’s possible to deliver the same value and service we do on Subaru vehicles on all  makes and models, and do not understand why or how any one else can claim to.   If you own a Subaru and need this repair which is probably why you are reading this I would suggest looking for an Independent Subaru shop.

The Head gasket we have had success with has been recently updated to help address the current trends and help make up for the loss in surface area. I want to stress that the best gasket in the world will only be as good as the repair method it self, and if not done correctly will not last.

Six Star Head Gaskets

In the video below I am demonstrating one very important reason to never let the Subaru Dealer or general repair shop make this repair on your Subaru unless you don’t have any other option.

At the Subaru dealer the Technicians are on a “Flat rate” pay plan, I will post a link here about how that process works (check back in the near future), but a quick explanation is the quicker you work the more money you make, but that’s only one aspect as a Subaru repaired under warranty when Subaru of America is footing the bill pays the Technician 40 to 50% of what they would make if you were the one paying the bill.   So if you’re a Tech working at a Subaru dealer and you had to make a head gasket repair under warranty is there any incentive to do a quality repair?  Any repair will last a year and that’s all it has to, but the difference between a quality head gasket repair and the quickest one possible could be the difference between one that lasts a year or two and one that never fails again.   So you’re the same technician and have now done 30 head gasket repairs under warranty and a “customer pay” repair finally comes in, do you slow it down, take the engine out and block sand it or do you make the repairs the same quick way you do for Subaru?

I point all of this out as the trend has changed a bit, we make less head gasket repairs now to the Subaru 2.5l, but each repair now demands greater attention to detail and almost every 2005 and newer is a customer pay situation as seldom do the head gaskets fail under warranty now.

I know Subaru and every other car maker likes to paint the picture that the Technicians at the Dealer are somehow better than the good independents, but that message is really just about marketing and is misunderstood by so many car owners.

Things that must be done to guarantee a long lasting repair are taking the engine out of the vehicle to make the repairs, there is no bending to this rule, it’s the single most important factor in the repair.  Subaru didn’t bolt the engine block into the car and then bolt the heads up to it, that would be silly, and it’s twice as silly to expect a good, clean, precise and long lasting repair if it’s done in the car.  The question is not can I, the question is should I?

Next the surfaces for both the Cylinder heads and engine block must be clean, smooth and free of any residue such as brake cleaner.  But most importantly need to be at a refinishing average of RA 50 or better.

FAQ.

Q: Does the engine need to come out.

A : Yes

Q: Only one side is leaking should I do them both?

A: Yes, do both the other will be the weak link if left alone.

Q: Do I need to resurface the heads

A: If they are warped, you are unable to check for warp or unable to refinish properly your self, YES

Q: Do I need to replace the Head Bolts?

A: If you are unable to check the bolts for stretch then yes, if you have a 2005 and newer, YES

Q: Which Head Gaskets Should I use?

A: If a good Independent Subaru  Shop is located around you, most likely the Six Star gasket will be your best bet, however if not the only other option is the OE Subaru Gasket, anything else will just not last.  I will add that it is always best to use which ever gasket the shop making the repairs has a good comfort level with.

Q: Is Subaru paying for this?

A: The WWP-99 campaign has ended, there are some cases where Subaru will participate after the 5 year 60,000 mile powertrain warranty has expired but its on a case by case basis. But understand any repair made at a Dealer will be done by someone in a hurry using the same gasket you already tried.

Q: How much does a Head Gasket Repair Cost if I have to foot the bill?

A: This is a very tricky thing to answer.   Labor can differ greatly across the nation just like home prices.  I have observed invoices from shops in Montana for $1000.00 and ones form New York for $3000.00.  You are much better off finding a good Subaru shop that charges a fair price and does a good job and obtaining a price from them.

Q: What can I do to prevent the head gasket problem form ever happening?

A: Maintain your Subaru based on how you use it! Cars that make frequent short trips will end up with a gasket failure much sooner than a commuter car with high miles.  This is almost always because of the lack of understanding of the definition of severe use and how short drives are your car’s worst enemy.  Don’t ignore check engine lights, stay on top of the cooling system service intervals, maintain proper oil change intervals (again based on how you use the car).  Never use any special oil or cooling system “fix in a bottle”, the symptom may be temporarily resolved but at a much higher price later. We have seen the wrong type of stop leak lead to replacement of everything in the cooling system such as the heater core, hoses and radiator on top of replacing the head gaskets, resulting in a very large repair bill.  Oil treatments that soften oil seals can accelerate the deterioration of the head gaskets very quickly.

The truth is that while you may do everything right and still end up with an issue, the  life of  the head gasket will be prolonged if you take the time to understand you own a piece of machinery that must be maintained based on real world use.  I say this all the time; we have several customers that have still never made a head gasket repair to their 2000 and later  Subaru with 200k and counting, and we have some customers that found us for the first time at 61,000 miles after being informed they had a head gasket leak.  The main variables are the driver and the use.  Proper maintenance costs more, and that’s just not popular, as a result the market place just doesn’t allow for it.

Here are a few more  pictures of some of the important points to a head gasket repair.

Taking the engine out allows for  better control when torquing the head bolts.

Torquing Head Bolts

Adjusting the valves while its all apart contributes to a complete repair and will help maintain economy and power.

Adjusting Valves on a Subaru

The head gasket repair will only be as good as the prep work, the left side of the cylinder head below is what many shops and dealer feel to be ok, when in reality the surface on the right side will yield much better results.

Subaru Cylinder Head Surface Prep

The Cylinder heads and engine block surfaces must be checked for warp and corrected as needed.

Checking Subaru Heads For Warp

Thanks for taking the time to read about the current trends with the Subaru Head Gasket situation.

If you have questions please post them here. I will as always do what I can to help.

Justin Stobb

Helping You get more out of your Subaru!