Spark plug tube seals: Why can't Subaru fix this?

[copyboy311]

I changed the spark plugs over the weekend to discover some oil on my old plugs and on the coil boots, some more than others. (Plugs looked pretty good still for 107k miles, but new ones improved the start-up response.)

 

I had this same leaking seal issue on my 2003 Legacy, and I see numerous complaints about other owners having leaking tube seals in all of Subaru's models. In over a decade of engineering, Subaru can't redesign a problematic spark plug tube seal?

 

I put in my new plugs and cleaned up the oil, but am not going to do anything about it now, as it's not such a big leak that it's causing misfire or leaking out the top. It's beyond my skill set and/or patience to do it myself. I assume it will be a pricey repair if and when I need to have it done by a professional. Anyone else have experience "ignoring" this problem?

Edited August 26, 2019 by copyboy311

[AWDFTW]

It's not a Subaru problem really. Gaskets wear out over time. I've never had a vehicle that didn't start leaking from the valve covers or something eventually.

[copyboy311]

It's not a Subaru problem really. Gaskets wear out over time. I've never had a vehicle that didn't start leaking from the valve covers or something eventually.

 

I respectfully disagree on this one. It seems to always be the tube seals that fail. I'm at 107k with leaks, and I don't know how long they've been leaking. My valve cover gaskets are fine, and so were the ones on my 2003 with 178k miles.

[cww516]

I think the issue is that heat and time aren't particularly kind to the seals. They're constantly below the oil level, too, which helps push oil out and make the issue more apparent, same with weeping head gaskets and such. When I replaced the seals in my Baja at 11 years / 173k miles, they felt like they might shatter if I dropped them on the floor. Replacing valve cover gaskets and spark plug tube seals isn't a terrible job, although it's definitely easier to do with the engine on a stand. If you can get your arms in there to do plugs, you should be able to handle pulling the valve covers and related gaskets, too, should you decide to give it a shot.

[TwoTone]

It's not a Subaru problem really. Gaskets wear out over time. I've never had a vehicle that didn't start leaking from the valve covers or something eventually.

 

 

No they don't, gaskets are forever just Subaru does a crappy job on those

[FLlegacy]

No they don't, gaskets are forever just Subaru does a crappy job on those

Gaskets are not lifetime parts, that's why there is auto parts stores that stock them. If they weren't necessary there would be no market for them. My LGT is 10 years old and doesnt leak at all. Even our Tribeca with 173k miles never leaked in the spark plug tubes. Same for my previous forester.

 

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[AWDFTW]

I respectfully disagree on this one. It seems to always be the tube seals that fail. I'm at 107k with leaks, and I don't know how long they've been leaking. My valve cover gaskets are fine, and so were the ones on my 2003 with 178k miles.

 

If you say so. Gaskets and seals degrade...it's a thing that happens. All my Subaru's have leaked eventually, usually from the valve covers or plug seals or headgaskets (ok, that one is an actual flawed material usage on the old single layer type). So have my Fords, the Oldsmobile, the Toyota...

 

No they don't, gaskets are forever just Subaru does a crappy job on those

 

In what fantasy land do materials not degrade with time, temp, and usage? Cause I want to buy my next car from there and bring it here to the real world.

[dgoodhue]

The flat boxer engine design is particular harder on gaskets due be more in oil bath and the not have oil drip drown like in an inline or V engine.

 

I am sure there must be a solution to improve the gaskets, but it probably involves more expensive gasket. The factory gaskets do usually last well past the warranty period, which is probably good enough for the bean counters...

[YeuEmMaiMai]

had the same issue on my Honda, tube seals always leak well before the valve cover gaskets did. i always replace both at the same time

[Falcor]

Show me a 4.0L Jeep with a dry rear main seal and valve cover. Sometimes it's design, sometimes it's assembly, sometimes it's material.

[copyboy311]

Show me a 4.0L Jeep with a dry rear main seal and valve cover. Sometimes it's design, sometimes it's assembly, sometimes it's material.

 

I dunno. I had a 4.0 Cherokee with 140k miles (bought it with 20k, so I know the gaskets were never replaced), and I don't recall if the rear main weeped, but it certainly didn't leak drops of oil. Same for the valve cover. No oil spots on my driveway, and they stopped making that engine in what, 2003? I'm talking about an engine Subaru still makes and still has the same issue.

 

The Subaru tube seals just seem like a very common problem that could be addressed; along with all the other Subaru quirks. I used to be a Subaru defender, but having now owned four of them, I'll buy something else for my next car. They no longer have a lock on the AWD market. My 2011 now has 107k miles, but has had many annoying things go wrong with it, seemingly a bit too soon. Two wheel bearings, cam seals, clutch at 95k (this is not a GT), a/c leak somewhere, spark plug tube seals, steering wheel radio controls no longer work, the exhaust shields that always rattle themselves loose, etc. I guess I haven't had the head gasket issue, so that's good.

 

I'm not going to fix the tube seals until it starts misfiring or leaking at the valve cover. We'll see how it goes, I guess.

Edited August 27, 2019 by copyboy311

[Falcor]

Sorry you having issues with your car. My 2011 is within 1k of 90k and I have had none of those issues. Granted, I bought it at 67k, but the PO took great care of it. It does have other quirks though.

 

I noticed you are in Wisconsin, so that may factor into the exhaust shields and wheel bearings.

[ArmyVetMP]

I should probably check my Spark Plugs and such.. I'm at 237k miles on my Legacy and to my knowledge, have never had the spark plugs changed.... lmao

[dgoodhue]

I dunno. I had a 4.0 Cherokee with 140k miles (bought it with 20k, so I know the gaskets were never replaced), and I don't recall if the rear main weeped, but it certainly didn't leak drops of oil. Same for the valve cover. No oil spots on my driveway, and they stopped making that engine in what, 2003? I'm talking about an engine Subaru still makes and still has the same issue.

 

Subaru currently only makes the EJ25 series for the STI. The last year for the 2.5i EJ253 was 2012.

[Alexmed2002]

I should probably check my Spark Plugs and such.. I'm at 237k miles on my Legacy and to my knowledge, have never had the spark plugs changed.... lmao

 

Wowza, that's a long time with stock plugs . I'm assuming your car starts up and drives great

[copyboy311]

Subaru currently only makes the EJ25 series for the STI. The last year for the 2.5i EJ253 was 2012.

 

OK, well they still offer a 2.5i on the base 2020 Legacy. How different could this engine be from the one ending in 2012?

[A_A_ron]

The 2.5i cars are the FB25 motors I believe. So quite a bit different.

[copyboy311]

The 2.5i cars are the FB25 motors I believe. So quite a bit different.

 

Ah, so an opportunity to fix the plug tube seal issue!

[dgoodhue]

OK, well they still offer a 2.5i on the base 2020 Legacy. How different could this engine be from the one ending in 2012?

 

It is a newly designed block and doesn't share parts with the prior generation. The FB25 is long stroke design with Timing Chain, the EJ25 was a Big Bore design with timing Belt.

 

https://www.caranddriver.com/news/a15126251/subaru-fb-series-engine-subaru-flat-four-engines/

[Falcor]

Our new Forester has that new 2.5L. So far so good. Of course, it's only got like 150 miles on it.

[SchwarzeEwigkt]

Practically every car I’ve ever had that the spark plugs went through the valve cover needed spark plug tube gasket and valve cover gaskets some time between 75k and 150k. My Ford, my Chryslers, my BMW, my Audi, my Subarus all needed them. I can only think of one that didn’t, which was my ‘05 Forester that got new valve cover and spark plug tube gaskets when the dealer replaced the head gaskets at 80k to fix the inevitable leak. I don’t know that it counts, but it’s not leaking even as it sits dead next to my house while I blow off selling it.

 

It’s a materials science thing, not a Subaru thing.

 

 

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[Herda2448]

Well I can’t say much but I changed my spark plugs the other day after just crossing over 140k on my 2012 2.5i 6mt. (Dealer replaced them at 80k when I bought it)

Anyway. I pulled the coils off to find oil around the tube seals and all over the bottom of the plug. I cleaned out the plug tube with a rag cause it was pooling in the tube. Although the top of the used plug was dry, this still doesn’t help me sleep well at night.

 

That’s being said. Would this oil build up be caused by “blow by” in the cylinder? If so, what can I do about this?

I know most catch cans are meant to turbo charged vehicles due to much more pressure than my NA 2.5.

I am always looking to tinker and learn so please don’t hold back.

Much appreciated in advance.

 

 

 

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[dgoodhue]

Well I can’t say much but I changed my spark plugs the other day after just crossing over 140k on my 2012 2.5i 6mt. (Dealer replaced them at 80k when I bought it)

Anyway. I pulled the coils off to find oil around the tube seals and all over the bottom of the plug. I cleaned out the plug tube with a rag cause it was pooling in the tube. Although the top of the used plug was dry, this still doesn’t help me sleep well at night.

 

That’s being said. Would this oil build up be caused by “blow by” in the cylinder? If so, what can I do about this?

I know most catch cans are meant to turbo charged vehicles due to much more pressure than my NA 2.5.

I am always looking to tinker and learn so please don’t hold back.

Much appreciated in advance.

 

 

 

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It isn't blow by or crank pressure (catch can). It is caused by leaking spark plug tube seals. You have to remove the valve covers to fix the problem. (valve cover gaskets should be done at the same time.)

[TwoTone]

No they don't, gaskets are forever just Subaru does a crappy job on those

 

Gaskets are not lifetime parts, that's why there is auto parts stores that stock them. If they weren't necessary there would be no market for them. My LGT is 10 years old and doesnt leak at all. Even our Tribeca with 173k miles never leaked in the spark plug tubes. Same for my previous forester.

 

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Sarcasm.

[SchwarzeEwigkt]

Well I can’t say much but I changed my spark plugs the other day after just crossing over 140k on my 2012 2.5i 6mt. (Dealer replaced them at 80k when I bought it)

Anyway. I pulled the coils off to find oil around the tube seals and all over the bottom of the plug. I cleaned out the plug tube with a rag cause it was pooling in the tube. Although the top of the used plug was dry, this still doesn’t help me sleep well at night.

 

That’s being said. Would this oil build up be caused by “blow by” in the cylinder? If so, what can I do about this?

I know most catch cans are meant to turbo charged vehicles due to much more pressure than my NA 2.5.

I am always looking to tinker and learn so please don’t hold back.

Much appreciated in advance.

 

 

 

Sent from my iPhone using Tapatalk

 

 

 

The oil in you spark plug tubes isn’t blowby. It’s leaking around the spark plug tube gaskets. They’re constantly soaked in the oil being pumped into the valve cover to oil the cans and other valve gear. If it was coming from inside the cylinder, you’d have two major problems. First, your spark plugs would be loose enough to allow the gas to come out, which would mean you’d have have compression issues at the very least. Further, you’d hear it when you (tried!) to run the engine. Second, there’d need to be enough oil getting into the cylinder for that to happen, meaning your rings were shot or you were somehow getting a whole bunch of oil in the intake stream or through the valve stem seals. Likely, it wouldn’t run at all and if it did, it’d run really badly with tons of blue smoke out the back. Luckily, that’s not the problem at all!

 

As for catch cans, I can’t remember the exact reason why they’re so much more useful on turbocharged cars than naturally aspirated ones, but suffice it to say there’s more oil vapor in the crankcase gasses of cars with forces induction engines. You certainly *can* put a catch can on an NA engine and it’ll definitely catch some oil that normally would get injected into the intake air stream. A friend of mine put one on the 6.4L HEMI in his Charger. He said he’d empty about a shot glass worth of oil from it every two or three weeks. The engine was pretty new, though, so more blowby would be normal there.

 

Will a catch can reduce the amount of oil that ends up in your intake tract? Probably. Is it worth it? Up to you, but good catch cans cost quite a bit. Personally, I feel like if you’ve got enough oil vapor coming out that you need to go out of your way to separate it out, you’ve got bigger problems than a catch can will solve. Plus, you’ve gotta monitor it; it gets full, you’ll start sucking that oil up there anyway.

 

I figure there’s a reason why you hardly see anything like that on production engines. It’s probably because it’s really not necessary. Closest thing to a catch can I can think of is what BMW does (did?) with their overcomplicated execution of their PCV. Several of their engines have a “crankcase ventilator,” known colloquially as the CCV. It does the same thing as a traditional PCV, but includes a nautilus shaped oil separator thing and some sort of pressure equalizing diaphragm. They’d collect crankcase vapor, condense the oil out, then route it back to the intake tract to burn whatever didn’t condense. The condensate would get routed back to the oil pan via a tube connected to the bottom of the dipstick. It reduces emissions. When it works. In practice, the oil separator would get sludged up in colder climates and clog. That’d cause the diaphragm to tear and put full engine vacuum on the dipstick, which would suck the oil out of the pan and deposit it straight into the intake manifold. You can imagine the smoke show that would make, I’m sure! Often, the dipstick tube — which was double walled, with the interior space for the stick and the annular space reserved for collecting what came out of the oil separator — would clog due to that annular space being kind of narrow, meaning the oil condensate would have nowhere to go but into the intake manifold anyway, so the whole purpose was defeated. If that didn’t happen, the half-mile of hoses and tubes connected to the stupid thing were made out of the very best plastic the Bavarian beancounters were willing to spec, so they’d regularly cause vacuum leaks which would lead to an increasingly lean mixture and eventually a check engine light that’s maddeningly difficult to diagnose correctly. Ask me how I know!

 

That catch can might be more worth it on purely direct injection motors, that is ones with no port injectors. Since you don’t have gas with detergents getting sprayed on the intake ports and valves, any oil that gets up there is liable to stick on there and turn into nasty carbon deposits you’ll have to scrub or walnut-blast out later. My dad has a newer BMW with a DI turbo-four in it that he put a catch can on specifically for that. Apparently, German DI motor’s are famous for coking up and needing a decarbonization every 30k or so. I don’t know if the FA and FB motors with the DI heads also have a port injector for cleaning. There’s hope they do, since Toyota puts a cleaning port injector on their DI motors and Subaru probably cribbed their DI tech from Toyota when they did the partnership that became the BRZ.

 

Er, yeah. I typed a lot there. Rambled, even.

 

TL;DR: It’s definitely not blowby, it’s just your spark plug tube gaskets. Catch cans probably are a waste of money for an NA car. Maybe less so if you’ve got direct injection.

 

 

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Edited September 5, 2019 by SchwarzeEwigkt