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Oil Burning Question/Problem (EJ25 DOHC)


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15 replies to this topic

#1 RallyKeith

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Posted 30 December 2005 - 09:23 PM

I've got a EJ25 DOHC motor that is burning on the order of 1 quart every 100-150 miles. When driving it you do not really notice any smoke out the back, until you coast down a hill. If you are up to speed (40-50 mph) and you coast down a long or hill for something like 1/8 mile, and get back on the gas a big cloud of smoke erupts from the tailpipe. Now everything I know tells me that this is valve guide seals, but I wanted some other input before I go tearing apart the motor.

Thanks,
Keith

#2 Snowman

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Posted 31 December 2005 - 01:06 AM

Have you replaced the PCV valve with a genuine Subaru one? This is a common problem, even on the newer engines.

#3 tunered

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Posted 31 December 2005 - 01:12 AM

i dont think valve seals could let that much oil by in that amount of miles,my guess is the tension is out of the rings from a previos overheat.jmho

#4 RallyKeith

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Posted 31 December 2005 - 07:02 PM

Have you replaced the PCV valve with a genuine Subaru one? This is a common problem, even on the newer engines.


It was replaced just for the sake of and was not bad.

This engine was recently installed in my car using the car's existing intake manifold and PCV valve and the old engine did not burn oil.

#5 RallyKeith

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Posted 31 December 2005 - 07:10 PM

i dont think valve seals could let that much oil by in that amount of miles,my guess is the tension is out of the rings from a previos overheat.jmho



This motor has never been overheated that the original owner or I know of. I would think an overheat event hot enough to cause something like that would do a lot more than just that, plus I would expect to notice a decrease in performance if the rings were that bad. I've done a compression test and everything looked ok there. I don't have the tools to do a leak down test, but I suspect it would be ok.

Also, this motor was purchased from the original owner who had the heads rebuilt after a valve burned out and he had someone who was not a subaru mechanic do the work. I know that the valve guide seals are different part numbers from the intake side to the exhaust so I'm placing money on them having been swapped by the person who rebuilt the heads.

Also, this symptom I described is widely attributed to bad valve guide seals. I've talk to several non-subaru specific Mechanics I know and they all agreed. I'm looking for something I may have overlooked that tends to be subaru common or specific.

Thanks guys.

#6 ferret

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Posted 31 December 2005 - 07:28 PM

Remember I can't see nor touch this motor:

Since you already looked at the PCV valve, this is where the crankcase blowby gets sucked into the intake and burned. How about the fresh air intake to the case. Different years used different crankcase ventilation systems. Could be you used the intake from your 'old' engine and the new engine had the crankcase vent either in the rear block or valve cover.

In either case, I would look into the fresh air inlet side to the crankcase first to ensure you have fresh air flowing into the crankcase then the PVC applies vacuum to remove the blowby gases. No inlet side results in the PCV being the only means to control crankcase pressure and ends up burning a lot of oil. I've seen this when the inlet 'filters' on other vehicles get clogged. Subaru usually has the inlet on the 'filtered' side of the air filter.

Only other cause, since it happens during decelleration are valve seals. If it were the rings, in particular the oil ring worn, usually the engine burns oil during accelleration and decelleration.

#7 grossgary

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Posted 31 December 2005 - 08:32 PM

if crankcase ventilation was this bad of an issue, i would expect your oil stick would likely be popping out an inch so. does it ever do that?

if that much oil is getting into a cylinder i would pull the plugs and see which one/ones are getting terribly fouled. that will tell you if it's related to one head or one cylinder or if it's not cylinder related at all.

#8 RallyKeith

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Posted 31 December 2005 - 09:36 PM

Everything Is hooked up the same way as it was originally. All the hoses go to the same things in the same places. Nothing was clogged and I don't see any differences in anything.

As for the dipstick (the car's, not me) it is never out or anything. It is always sitting fully down.

I think I'm going to tear it apart and see what I can find.

#9 nipper

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Posted 31 December 2005 - 10:38 PM

are you sure your not leaking oil? thats an auful lot of oil to burn and not have a smoke screen behind you, no matter how your digesting the oil.


nipper

#10 RallyKeith

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Posted 01 January 2006 - 12:25 AM

are you sure your not leaking oil? thats an auful lot of oil to burn and not have a smoke screen behind you, no matter how your digesting the oil.


nipper


Um, like my original post said:

If you are up to speed (40-50 mph) and you coast down a long or hill for something like 1/8 mile, and get back on the gas a big cloud of smoke erupts from the tailpipe.


I've looked and I can't find a single leak. All the cam seals and the rear main were replaced, if it's coming out of the valve covers then none of it is hitting the engine cross member as it is dry. I agree that it seems like a lot of oil, but I can't find any leaks.

Let me just sum up what I understand about oil consumption as it relates to rings and valve guide seals.
- If it burns oils, you see blue smoke, while you are on the gas and the RPMs are up it is most likely rings. As the oil is being splashed up on the pistons it is getting by the rings.
- If it burns oil during deceleration or shows smoke imediately after prolonged idle it is the valve guide seals. In this situation the engine is seeing high vacuum and it is pulling the oil right through the seals. The reason it might not smoke during actual deceleration is because most cars during decel (and while in gear) will not fire cylinders in order to increase fuel economy. As soon as you step back on the gas all the heavy oil that still in the cylider is burned.

Does any of this sound wrong? The more I think about/think over this the more I really think I'm just gonna be done with it and swapped out these heads for some known good ones.

Keith

#11 cookie

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Posted 01 January 2006 - 01:56 AM

On my last Mercedes the valve seals were different between exhaust and intake. I had a cam replaced by a local shop and they screwed up. The upshot was the cam drive bolt came off and bent the valves. They went good and pulled the head and had a local machine shop redo it. These folks revesed the seals and it burned oil like mad. Symptoms just like yours.
By this time I was tired of the issue and put new seals on in the basement. Oil consumption dropped to where it had been before the incident.

#12 '05 STi

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Posted 01 January 2006 - 07:44 AM

are you sure your not leaking oil? thats an auful lot of oil to burn and not have a smoke screen behind you, no matter how your digesting the oil.


nipper


I'm not real familiar with the EJ25, as this is my first Subaru, so if I'm way off base, don't shoot me. :) Have you considered that maybe it's a spun bearing? Are you losing any power?

FWIW, my dad has a 1989 GTA, and when the motor spun a bearing, the engine was internally eating oil. There was no "smokescreen." Eventually, the motor just lost a lot of power, and then stopped altogether.

#13 RallyKeith

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Posted 01 January 2006 - 12:14 PM

I'm not real familiar with the EJ25, as this is my first Subaru, so if I'm way off base, don't shoot me. :) Have you considered that maybe it's a spun bearing? Are you losing any power?

FWIW, my dad has a 1989 GTA, and when the motor spun a bearing, the engine was internally eating oil. There was no "smokescreen." Eventually, the motor just lost a lot of power, and then stopped altogether.


Welcome to the wonderful world of Subaru! Do you have an '05 STi as your name implies? I have an '04 STi

Anyhow, no spun bearings. Car runs perfect except for this. With a spun bearing or even a "loose" bearing you would get a knocking noise from the engine. This motor was installed because the previosu motor had loose bearings. When up to temp the old motor would kock a little.

I'm going with cookie on this. I'm betting someone reversed the seals.

Keith

#14 '05 STi

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Posted 01 January 2006 - 01:07 PM

Welcome to the wonderful world of Subaru! Do you have an '05 STi as your name implies? I have an '04 STi

Anyhow, no spun bearings. Car runs perfect except for this. With a spun bearing or even a "loose" bearing you would get a knocking noise from the engine. This motor was installed because the previosu motor had loose bearings. When up to temp the old motor would kock a little.

I'm going with cookie on this. I'm betting someone reversed the seals.

Keith


Gotcha. Thanks. :D

#15 RallyKeith

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Posted 05 January 2006 - 10:58 PM

Just as a revisit, I spoke to the head mechanic at my local dealership to ask advice. I wanted to see if they ever had a new tech swap the seals and how much oil it burned, or what else he thought I should look at. He said to start with a dry compression test and then a wet compression test (squirt a little oil in the cylinder) and if the numbers change drastically then it's a ring problem. He also told me that the difference in the intake valve seals and the exhaust valve seals is the material, not size, and that the intake seals can't take the heat the exhaust valves see.

Anyhow, I did the compression test and everything seemed fined. Numbers only changed on average about 20psi from dry to wet. So it looks like this weekend I'm swapping the heads.

Keith

#16 blitz

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Posted 06 January 2006 - 06:57 AM

Over the last year or so I've been seeing individual stories of 2.5's with abnormally high oil consumption like yours.

I'm beginning to wonder if it isn't due to a small batch of motors that left the factory with mixed-up seals.




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