98 Subi Forester - time for headgasket



I just do not subscribe to the bad block theory. If the engine block was the cause of the problem then it would be pointless to even change the head gaskets because they would be doomed to fail again due to the alleged bad block.

Another school of thought (not mine) is that the head gaskets themselves are of inferior design.

Properly done, head gaskets are good for the duration.


Well, something’s the problem, we get more questions here about bad 2.5l Subaru head gaskets than all other brands/makes/models combined, it seems.




Well, in my opinion the question is how many (if any) of the R&R’s are blowing the second head gasket? Right? As long as no one has seen the dreaded reedoo as a major issue here, then I would say the likely culprit is the head gasket itself. I mean, I think what ok4450 says about the head bolts makes sense too, but you could still point at a faulty gasket as the reason the head bolts need to be re-torqued.


“I don’t consider Subaru head gasket problems a design flaw so much as a process flaw. If head bolts were retightened after some time in operation (say 500-1000 miles) odds are these problems would never surface” - OK4450

OK, with great respect, I would consider any design that requires retightening of the head bolts after 500-1000 miles as being a flawed design. The market for which the car is designed is comprised of people for whom retorquing head bolts is entirely alien. If all engines from all manufacturers required this maintenance, I’d not consider the weakness a flaw… but they don’t. So I do.

I should perhaps clarify that I consider the manufacturing process an integral part of the design package. And once the car leaves the manufacturer, there should be no additional assembly processes needed. Only maintenance.


Just a few comments clipped short to avoid lengthening the post.
Faulty head gaskets are claimed due to part of the gasket material rotting out. Hot coolant is corrosive and a seeping gasket will get eaten by the coolant no matter the make of car. This can also actually eat the cylinder head surface up, take out valves and seats, etc. That’s my reasoning for not going along with the faulty head gasket theory. Head bolts tight, no seepage, no problem.

I personally think one design issue is when Subaru went from 8 bolts to 6 bolts per head and combined with a lack of head bolt retorque the problems surface.

Even Fel-Pro states that many gaskets require a retorque of the cylinder head bolts no matter the make.

The dates are fuzzy but back in the mid 80s Subaru had no head gasket problems unless the engine was overheated. Subaru issued a bulletin stating that head bolt retorques were no longer necessary ONLY on cars with automatic transmissions. Still required on manual cars even though both used the same engines, same head gaskets, and same head bolts.
So what happened? The automatic cars started leaking oil from the head gaskets. This led to another bulletin which stated the head bolts should be retorqued.
Eventually another bulletin a few years later stating no longer necessary. This was followed by the where we’re at today scenario…

All metal changes its characteristics with heating and cooling cycles and combined with gasket crush and relaxation head bolts losing a bit of their snugness is not that rare.
It also occurs with valve cover or oil pan bolts, etc and there’s a reason why even Wal Mart tells tire customers to return for a wheel lug retorque.
The fact those wheel lugs are torqued to 70 Ft. Lbs does not mean they will be close to 70 or those valve cover bolts will be at the same torque the next day.

When you’re dealing with iron things can remain fairly constant. With soft products, alloys, or aluminum involved not so much.


I should have added that some factory service manuals also consider retorquing the head bolts a valid method for stopping leaks.
Retorquing the head bolts before the leaks begin is ideally a good way to make sure they never start.


Thermal expansion coefficients are higher with aluminum and its alloys than with cast iron, but that does not absolve the designers from compensating for the coefficient differences in the design. Including the gaskets. and including thermally induced cold flow of the gasket material. Retorqueing headbolts after purchase is not required of any other engine and should not be required of Subies either. Modern computer programs have built into them the capability to do all of the thermal mapping, finite element analysis, and everything else necessary for engineers to have designed this problem into history… retorqueing the headbolts is just a bandaid, not a fix.

The problems resulting from going from eight headbolts to six headbolts should not have happened. Not with the design programs that have been in existence for the last 30 years. There’s no acceptable excuse.

I’m fully aware that it happens with all materials, and if I still had the ASME standards lined up next to me in a technical library I could tell you exactly how much for each material. If you think problems from it are impossible to avoid in an automobile engine, you should have been part of our team that designed active sensors that mounted on the afterburner shrouds of the engines that went in the F-15s and F-16s. We were dealing with extreme temperatures combined with extreme vibration. And the components included not only steel and aluminum, but polyimide-amides, silicone silastics (yes, combined with glass spheres they can be made to withstand high temperatures), a high temperature plastic called Torlon, and even a hermetically sealed tube with a fused quartz bulb sensing through a fused silica lens.

I lay the fault with the engineers. No place else. They were not “pushing the envelope”, they were designing a normal engine, albeit with a different cylinder layout. That’s not to be interpreted as meaning that I dislike Subies, because I don’t. It only means that I consider the headgasket problems to have been solely on the shoulders of the engineers.

By the way, thanks for bringing back some great old memories. That was a truly great team we had. The best bunch of guys I’ve ever worked with. Some of us received formal awards from Pratt & Whitney’s design group out of Florida for our parts in the design, but the truly great thing was the guys. A more eclectic group I’ve never seen.


I understand the theoreticals but in practice things often work out differently. Most head gasket manufacturers recommend a head bolt retorque and this would have nothing to do with Subaru or their engineering team though.

The procedure I’ve used with Subaru head gaskets is the following and there have never been any issues afterwards.

Clean mating surfaces of block and head squeaky clean with a small razor sharp putty knife or razor blade. NO gasket scrapers.
Check cylinder head for warpage and surface as necessary. A .002 deviation is allowable but the preference is to take it down flat.
Replace valve seals at the time and perform valve job if high miles.
Coat head gaskets with aerosol Copper Coat.
Tighten head bolts per specs.
Allow to sit for a while; preferably overnight.
Retighten head bolts the next day. Odds are they will be found to have loosened a little.
Replace thermostat and change engine oil/filter.

There should not be any issues with HGs after that unless the engine is overheated.

Speaking of P & W, the 4360 Wasp Major is a marvel of engineering. I stood and stared (drooled might be a better word) at one of those things for a solid hour once and never got bored. I can’t even imagine how many man hours went into the design alone of that engine.
It’s the most fascinating engine I’ve ever seen in my life.


True, but when discussing the retorqueing procedures recommended by head gasket manufacturers you’re referring to engine rebuilds. New engines should not require the head bolts to be retorqued after delivery of the vehicle to the customer. If a retorqueing is necessary after the engine is run in, the run in and retorqueing should be done before installation into the vehicle… or at least before shipping the vehicle.

The most fascinating engine I’ve ever seen was a 28 cylinder radial engine from a WWII bomber (can’t remember which). It was four stacked 7-cylinder segments with enormous cylinders. It weighed 3200 pounds. Like the Wasp engine, it’s a piece of art.


At one time Subaru used to recommend a head bolt retorque and valve lash adjustment at the 1000 miles mark. This was done as a courtesy to the customer and free of charge.
There were no head gasket issues with these vehicles; unless overheated.

It sounds like we’re on the same page with the aircraft engine. That Wasp Major was 28 cylinders with 4 rows of 7 and displaced 4360 cubic inches. Dual magnetos and 56 spark plugs to change.

A few years ago at Hill AFB in UT I noted they had one in their museum that was a cutaway. They’re a total beast of an engine.
Now if someone could just shoehorn one into a Subaru… :smiley:


The general rule with torque-to-yield head bolts is that they are not reusable. They should not be loosened and re-torqued, the head bolts have been stretched and are not reusable. With the engine between the frame rails replacing the head bolts would be a major job for routine maintenance.


What is the status of the head gaskets on new subaru’s. Is the problem gone? As an owner, I have more than a passing interest.



The new (2011?) 2.5 l engine has no coolant passages through the head gasket, so the hope is the problem is solved.


A Subie? Why not? They’ve been put into motorcycles…


Id have to agree with you 4450. Since I’ve been thru this exact repair…I asked a few questions in the process. But Subaru as you can imagine got a lot of customer complaints from this since their vehicles usually did NOT have this issue.

Subaru themselves said they found some fault in the gasket… Now is this entirely the reason? I have no clue but I was told that the gaskets I was buying were NOT the same as the ones that blew on the engine.

Who knows… Like Ive said…none of mine have come back yet. A testament to me? I dunno…I am old school enough to know that I know what Im doing. I do also do my best and pay attention to detail…which is more than half the battle.

Honestly I DO want to know the real culprit behind all these blown gaskets…could very well BE the inability to re-tighten those original head bolts?


A Subie? Why not? They've been put into motorcycles....... http://www.bing.com/images/search?q=28+cylinder+radial+engine+images&qpvt=28+cyliner+radial+engine+images&qpvt=28+cyliner+radial+engine+images&FORM=IGRE

Well 7 out of 28 anyways. And quite unique at that.


Subaru head bolts are reuseable and they’re tightened to angle. For what it’s worth anyway, I’ve never replaced head bolts on a Subaru head gasket job and have never had one come back to bite me.
Subaru makes no mention of replacing the bolts and in all honesty, tightening the head bolts originally actually involves a re-torque so to speak.

Speaking of aircraft/car engine swaps, do a net search for the Australian who stuffed a P-51 Mustang Merlin engine into a '55 Chevy. Pure genius and a work of art. :slight_smile:


Wow! That’s news…ok4450, you DON’T replace the head bolts? I wondered about that - think about it - if the original problem is the new bolts are stretching a bit too much, resulting in a blown HG, why NOT use the old bolts?? It actually makes MORE sense to use the old bolts.


Honda, you’ve brought up a very real possibility, that it’s a parts problem rather than a design problem. That makes sense to me.

My main argument was that head bolts should not have to be retorqued after vehicle purchase, but I may have unfairly placed the blame on the Subie engineers when it may have been a vendor problem.