Subaru 2.5 L engine - the worst engine ever?

The Subaru 4 cylinder 2.5 L “Boxer engine” has had numerous problems with head gasket (HG) coolant leaks.

The HG problems are outlined on the website http://use…asket.html


1. The HG leaks occur in 2.5 L engines manufactured since 1996. Subaru claims the problem was corrected after 2002, but complaints are still being made on later models.

2. The 1996 to 1999 2.5 L Dual Overhead Cam engine had an inadequately designed HG which often failed early in the life of the engine. The failure allowed coolant leakage into the cylinders, which often went undetected and resulted in over heating and engine failure.

3. The 1999 to present 2.5 L engine has a Single Overhead Cam. This engine also had, and may still have, an inadequately designed HG which fails early in the life of the engine. In this engine, the failure allows external coolant leakage, which can also result in over heating and engine failure.

4. Subaru recognized the HG problem in the 2.5 L SOC engines and in April 2002 implemented a “Service Campaign” to “fix” the problem, which Subaru claims only occurred in 1999 to 2002 model years. It is clear that the inadequate design of the head gaskets resulted in early external coolant leakage failures in numerous vehicles.

5. The “Service Campaign” for the 1999 to 2002 2.5 L SOC engine consisted of adding “Genuine Cooling System Conditioner” (i.e. stop leak) to the coolant and extending the engine warranty to 8 years or 100,000 miles.

I have a 2000 Subaru Outback Wagon with the 2.5 L SOC engine.

When I received Service Campaign bulletin in April 2002, I had the dealer add the “Genuine Cooling System Conditioner” to my cooling system.

However, now at approximately 114,000 miles, coolant is profusely leaking through the poorly designed head gaskets.


1. The coolant leakage problem that occurs in 2.5 L Subaru engines is a result of inadequately/poorly designed head gaskets.

2. Without intervention, at least one head gasket in the 2.5 L engine is expected to fail in the life of nearly all 1999 to 2002 vehicles (estimated 90%probability at 100,000 miles).

3. Essentially, the head gasket failure is the result of an initial design flaw that manifests as a “latent failure”.

4. The addition of the “Genuine Cooling System Conditioner” simply delays the failure of the inherent design flaw.

5. If a failure occurs after 8 years/100,000 miles, Subaru does not take responsibility for head gasket leaks.

6. The design flaw was inherent in the 2.5 L engine at the time it was manufactured. The design flaw results in a latent failure of one/both of the head gaskets. Adding “Genuine Cooling System Conditioner”, as directed by Subaru, simply delays the HG failure and covers-up the fact that the 2.5 L engine is inherently unreliable.

7. The cost to repair this failure is approximately $1,500, assuming no internal engine damage. Nearly every Subaru vehicle with this design flaw will need to make this repair. Approximately 385,000 vehicles were in the “Genuine Cooling System Conditioner” (WP99) recall. At $1,500/vehicle, that’s a total cost to consumers of nearly $600 million.

Subaru has masked the problem by having owners add stop leak as a temporary “fix” to a serious reliability problem.

This has resulted in very large costs to Subaru owners who must pay for repairs that resulted from a time zero design defect.

Head gaskets fail on other engines, too; the 2.5L Subaru is not the only one. I agree that this engine has a reputation for head gasket problems, but I’ll bet you’ve had close to ZERO problems with your Subaru until now.

The car is nine years old and has 114K miles on it. What do you want?

Fix it or sell it. Your choice.

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I concur the 2.5L Subaru engine (non-turbo) has head gasket issues from 1996-2004(not present). However they seem to have stopped in 2005 where the engine design changed a bit. This is even evident in Consumer Reports which shows major engine problems for all the models (except turbo) only up to 2004. The major engine problem is the head gasket. The rest of the car earns high marks.

The $1500 while quite steep could be worse like a sludged motor($3000-$5000) of early 2000’s Toyota or early 2000’s Honda automatic($3000+).

Subaru should have fessed up more and made the warranty 8yrs/150k not the 8/100k.

The coolant conditioner a diluted stop leak that gives Subaru insurance to the problem across all models.

The turbo 2.0L(2002-2005 WRX) and 2.5L turbo(2004-present) are immune to head gasket problems in any significant #.

That being said my family has 4 Subaru’s with the effected engine and anywhere from 100k-200k and not a single cooling problem. They do maintain the cooling systems though. So your logic they all fail is not true. I just believe it is a high percentage like 30%+ not 100%.

It’s a well known problem. But plenty of other cars have issues as well. Ford’s 3.8L has an even worse head gasket problem in addition to problems with the aluminun valve bodies in the transmissions used in the Taurus/Sable and Windstar. Dodge has tranmission problems with their “Ultradrive” transmsission in the late 80’s and early 90’s. The 3.1/3.4L GM V6 had a well know intake gasket problem. Toyota and VW had problems with sludge build up in their engines a few years ago.

The point is no automaker makes a perfect car, even the ones with a repuation for great reliability. Subaru stepped up the plate and offered to cover repairs for 8 years or 100k. That’s a better offer than most other automakers offer.

I can’t help but notice, that the turbo models (WRX, Forrester XT) don’t seem to be affected. I guess that’s because the used lower-compression pistons/heads on those. Strange that a tubrocharged car would end up having fewer problems that it’s N/A counterparts.

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This thread belongs in the Rant-N-Rave section (if they still have it), not here in the area for actual car questions.

Subarus were having head gasket problems 30 years ago and then as now, Subaru denied there was ever a problem. Subaru even had a service bulletin issued way back when stating there was not a problem with their head gaskets (marketing dept. at work) but would cover them “if the customer squawked enough”. Not phrased like that but you get the point.

JMHO here, but I feel the problem is a bit deeper than head gasket design. They’re using 6 head bolts per side as compared to the earlier (and generally trouble free) 8 bolt design.
Another factor is lack or a head bolt retorque at a very low mileage. In theory torque to yield bolts should not be retorqued. In practice it may be a different matter since every metal known to man changes its shape over time.

I will add a good source of info on headgaskets in non turbo 2.5L subaru is here->

Been a year since the last post on this thread. But the problem is still with us.

In the past 10 days three Subaru’s, 2001, 2002, 2003 that I had checked out by my mechanic on a pre-purchase inspection had the beginnings of head gasket leaks. As in my mechanic’s experience, all were on the left front of the engine. Mileage ranged from 91-115,000. Two Forester’s and a Legacy.

I have heard all the excuses, that other cars have head gasket failures, if we get to 100k miles what are we complaining about. All bosh. I have owned a lot of cars in my life. Take them to high mileage unless they get totaled, as my Prelude did at 190k. My first, a '62 Ford Falcon went to 219k. None of my cars ever had a head gasket failure, except my 1997 Outback where the head gasket failed around 120,000 miles. The prevalence of this problem is undeniable on Subaru’s of this vintage. It is shameful that the company let this go on for so long.

Just FWIW, the 3.8L is no longer made, and hasn’t been for years. But it was a lemon, arguably significantly worse than the Subaru.

And the widespread Taurus/Sable/Windstar transmission problems have been gone for 15 years…

I stumbled across your post after experiencing the same hg failure you describe. We own a 2001 Subaru Outback with the 2.5L engine and at 99,988 miles our hg failed. Keep in mind this is a 9 year old car that has been driven a little over 10,000 miles a year since it was bought. The conditioner was added to our car, but alas, the conditioner is not a problem solver/fixer. The hg was poorly designed. Instead of SOA owning their mistake in design (which I’m sure they decided to option to do the right thing for customers would cost too much since you have to remove the engine to replace head gaskets), they slap a band aid on the issue.

I will never buy nor recommend a Subaru to anyone. It is inexcusable to make a $30,000 car that require major engine repair before 150,000 miles. To not value the customer experience is even more revealing of Subaru’s company culture. I’m going back to Honda as soon as I get my 5 ton station wagon out of the shop. I refuse to drive a time bomb any longer.

I had a head gasket fail on my 1966 Impala. I forgave it; it was over 30 years old. What I want in particular is a car that costs more than my Honda to be as reliable if not more so. Otherwise, what am I paying for? Or what would even be better is a company that stands behind what they make by solving the problem, not duct taping a solution to buy time.

And be honest, a head gasket failing before 150,00 miles is rare for any car made 2000 on…unless of course you own a Subaru.

Yes, it’s a poor design. Yes, it’s disappointing to have that type of failure at such seemingly low miles. However, once the repair has been done the first time (assuming the use of high quality aftermarket (felpro MLS type are excellent) gaskets and quality workmanship from your mechanic), this will never be an issue again. And aside from that particular issue, they have very few common problems and will regularly last 300,000 to 400,000 miles or more. I own a 2000 outback with 277,000. We have a customer with an '01 outback with 425,000. It’s engine is just now getting tired. Very good cars if taken care of.

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Thanks , you just dragged up a 6 year old thread that has spam on it.


There was a thread here a while ago which suggested the subie head gasket quality isn’t the actual problem, but just that the head gasket in that engine design has a more challenging job to fulfill than other engine designs. B/c of the tight tolerances involved, resulting from an engine design objective to provide improved coolant flow through the engine. In other words bigger coolant passanges means less distance at the head/block interface from those passages to the combustion chambers, etc.

when I owned Subies, I bookmarked this article:

essentially: if owner neglects his car, this opposite-engine design will give up on these gaskets due to increased coolant acidity eating material away in this high-flow/high-pressure design and/or if grounding is not sufficient

it is indeed a predisposition for this kind of failure, as their 2.2 liter engine never had such issues, so in newer 2.5 they changed the way how channels with coolant go around and now it is way more material separating cylinder form coolant, at least at a point where head contacts the block, so headgasket topic is closed for good

I have my own opinions about why the head gaskets fail. If it was block design then this should mean that any head gasket replacement is futile.

I’ve done a lot of Subaru head gasket replacements and never had a single one come back.

Subaru EJ engines have numerous ongoing issues that Subaru refuses to address; head gasket failures, “ring land” failures, rod bearing failures, high oil consumption, etc. Any of these issues can, and often do lead to catastrophic engine failure.

So exactly what is the story behind this “ring land” failure?

ok4450 - Weak cast pistons, bad factory tune, engine knock among other things.

I can’t say that I’ve ever seen a case of ring land failure on a Subaru and the few that I’ve seen with a rod bearing knock usually had a history of few oil changes and/or running the engine low on oil.

If by engine knock you mean pre-ignition rattles that will definitely cause a piston problem. In most cases that’s caused by too low octane fuel (especially on turbocharged…) or by an EGR system fault.
That’s hardly a design flaw.