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Discussion Starter #1
Hey all,

I just recently bought a used 2010 Outback 6MT with 159K (now has 166K-I drive a lot) and it's great. However, I'm experiencing two major issues:

First, oil consumption. I just drove this thing from NY to Colorado and back. Prior, I did an oil change with STP full synth. About 1000 highway miles in, the (new to me) low oil light came on (not the red light, the yellow one). I looked at the manual and saw that it means the oil is about a quart low. Filled it up (it was true, dipstick reading told me so) and went on my business. It happened 3 or 4 more times on the trip. And it still happens. And it seems to be getting slightly worse, mileage wise.

The PVC valve was replaced by me with an OEM one. No change. In fact, it seems to have gotten worse since that too. I'm adding a quart every 700-800 miles or so. That is out of spec.

Secondly, upon arriving back, I got the P0420 code abour 50 miles after filling up one day. Pulled the code and it had 3, all the same, for P0420-bank 1. I've searched high and low and haven't seen many with gen 4 having solutions to this. Once PVC was replaced and the code came back, it now lists 2 instead of 3. The code disappears on its own and reappears on its own.

I'm well equipped to do any work this car might need-have done countless headgasket jobs and timing belts, etc. I'm definitely considered a Subaru mechanic on the side. I'd rather not replace piston rings on a 2010, but hey.

Oh and for the oil issue-I can find no external leaks whatsoever.
 

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I have never heard of an EJ engine consuming oil. (GEN4 used EJ engine up till 2013 where the oil-consuming FB engine started to be used)

Are you CERTAIN the oil is not leaking somewhere?

Also, some oil brands tend to be 'consumed' faster than others. Have you tried a different oil brand? (5w40 is the correct oil for EJ engine)

Correction (Thanks Huxley): 5w30 or 5w40 is acceptable based on your driving climate. Certainly trying a heavier weight oil may reduce consumption.
 

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Discussion Starter #3
I thought the correct oil was 5W-30? And the EJ engines were known for consuming oil, especially as they age-just not like the FB series. As for oil brand, I just picked up the STP synth because it was on sale. I'll try Castrol or regular dino oil for the upcoming change and report results.

The P0420 code went off after filling the tank tonight. I really made sure the gas cap was on tight. I think it was coincidental, considering how many times it has illuminated in the past week and a half. I may buy a new gas cap for the **** of it though.
 

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From a little Googling, it seems the P0420 code means the exhaust is rich at the O2 sensor after the catalytic converter. Following that scenario, I would pursue the following possible causes:

1) The O2 sensor is malfunctioning. Nowadays, 100k miles is considered the life of an O2 sensor, and you're well beyond that. Replacing an O2 sensor is both cheaper and easier than the next 2 alternatives, so I would do that first and see if the code occurs again.

2) The exhaust gas is too rich due to a combustion problem. This could be poor combustion from any number of causes, such as a spark plug not firing, but I think you'd get other symptoms such as engine knock, power loss, and a drop in mileage. You did report a drop in mileage, so maybe. But you also report high oil consumption. I'm thinking oil is getting into the combustion chamber, and as a heavy hydrocarbon, its not burning completely and is making the exhaust rich. You already replaced the PCV valve, so this might be a blown head gasket, warped head, valve seals. Check the oil and coolant for signs they are also leaking and mixing. Watch the exhaust on start-up for the telltale cloud of blue smoke, especially on cold starts. While diagnosing this can take a lot of time, the cost of the true cause could be moderate, so I would investigate this second.

3) Your catalytic converter could be bad. This is the most expensive possible cause I've mentioned, so I'd check it last. And the damage could be from some other combustion problem, so I would investigate the things I mention in #2 also. You don't want to drop $2k on a new converter, only to have it damaged too by the same underlying cause.

Those are the thoughts of this shade tree mechanic. I've chased oil consumption problems in another car, and it can be a bit of detective work. I do think its likely the oil is somehow making its way into the combustion chambers.

Oh, one last thing, I would normally also suspect the PCV valve, but you stated you replaced it with an OEM unit already. Definitely a smart first move. In that other brand of car, it wasn't unusual for a vacuum leak elsewhere to cause the PCV system to suck oil from the crankcase and into the intake. I don't know if Subaru uses a similar system (IMHO over-engineered to the point of being difficult to maintain), but its something to consider as a possibility. I would get LEAN O2 error codes in that car (a BMW), despite the oil combustion, because so much air was entering the system after the mass airflow sensor.
 

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Discussion Starter #5
The P0420 code is on again.

And thanks for your reply.

For the cat-I found paperwork that proves replacement in the last 20-30K. If I did go that route, I certainly wouldn't drop thousands on an OEM unit-rockauto all the way on that one.

On this car, I believe bank 1 is the AF O2 sensor prior to the cat. Granted, it could be bad, but I think Bank 2 and beyond are the ones post cat. Someone correct me if I'm wrong there.

No blown headgaskets here. Subaru finally went MLS stock 2010 and beyond and they look to be holding up just fine. The engine is dry and there is no mixing (though on a Subaru, there is seldom mixing if it's an external leak-failing HG's on this car present differently it seems)

The oil consumption thing is more worrisome to me than the code. Once I fix the code, I still need to contend with that.
 

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rear o2 sensor is the one that makes the p0420 code.

AF and o2 sensors do get old and sooty over time, even if you have no issue making them that way other then just driving it.

I would change out the rear o2 sensor with a denso branded one.

________

the front ones make more and different codes. sometimes making a p0420 as in relation to the other codes.

_______

oil consumption. keep a eye on it, maybe go for 10w30 now that the weather is getting warmer.
 

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The P0420 code is on again.

And thanks for your reply.

For the cat-I found paperwork that proves replacement in the last 20-30K. If I did go that route, I certainly wouldn't drop thousands on an OEM unit-rockauto all the way on that one.

On this car, I believe bank 1 is the AF O2 sensor prior to the cat. Granted, it could be bad, but I think Bank 2 and beyond are the ones post cat. Someone correct me if I'm wrong there.

No blown headgaskets here. Subaru finally went MLS stock 2010 and beyond and they look to be holding up just fine. The engine is dry and there is no mixing (though on a Subaru, there is seldom mixing if it's an external leak-failing HG's on this car present differently it seems)

The oil consumption thing is more worrisome to me than the code. Once I fix the code, I still need to contend with that.
I am pretty sure your Subaru engine has only BANK1. (There is no BANK2) Generally, a multiple 'bank' of cylinders is found on VEE-style engines (V6, V8)

I am also pretty sure there are TWO O2 sensors.
1) Before the CAT
2) After the CAT

The one BEFORE the CAT is used by the ECU to 'tune' the engine so it is running most efficiently. The ECU alters ignition, injection and other variables to achieve this. If the ECU is not able to achieve stoichiometric conditions, a code will be set and the CEL will be illuminated.

The O2 AFTER the CAT has only a single use. To test the efficiency of the CAT. If the CAT is not able to do its job, a code will be set and the CEL will be illuminated.

Each CEL code specifically points to where a problem was detected.

BEWARE: The CEL codes do NOT tell you what is bad... ONLY where a problem was detected. It takes an understanding of the OBDII system and engine-dynamics to isolate a problem. (Just because an O2 sensor detects a problem DOES NOT mean the O2 sensor is bad.... dont blame the messenger!!)

Knowing the above - you should be able to troubleshoot and isolate your issue without throwing parts at it.
 

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use an infrared thermometer and try to measure temps immediately before and after the car after the car has warmed-up. compare to a car with no codes also?) the temp after the cat should be higher than the input temp. Some say the output temp should be at least 75*F higher than the input temp. If it is, then perhaps the after cat sensor is bad. If it isn't, the the cat is not 'lighting-off and may be bad - but many folks have found exhaust leaks or engine 'tune-up'/running problems that prevent the cat from working.. Cat. convs. are pricey, just make sure it's bad before swapping it.
 

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Discussion Starter #9
It's off again. What I'm currently doing is ordering a Denso branded rear 02 sensor.

Here's some info I found on the car:

In 2014, at 111K, a Subaru dealer replaced the "catalyist" converters (their spelling, not mine). Complaint was "check engine light is back on".

Looks as though there was no charge to the owner.

Then, not quite a year ago, in April of 2016-this poor PO had the catalytic converter replaced AGAIN. This time it was done at an independent shop. Looks like she paid just over $1200. 1100 for parts, 100 bucks for labor. Looks like the check engine light was on again and the shop just went for the converter option, again.

Nowhere on either receipt do they list replacement of any O2 sensor. At all.

So, eagleeye convinced me in another thread. Gonna replace that rear one and see if that settles that issue. After, I gotta tackle the oil consumption. It is HIGH. Like, 600 miles/1 quart high. I still don't believe it's a leak.
 

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A quart every 600 miles is a lot. That is to the point where I would expect a blue plume of smoke to be following you down the road.

If that is going out the exhaust I would expect both the converter and the O2 sensors to have rather short lives.

I'm not so sure the oil consumption isn't the first issue you need to resolve.
 

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when you pull the rear o2 sensor, maybe pull the front one (A/F) just to look at it for oil. = confirming you are loosing oil into the exhaust and it is getting burned up by the cat converter.
 

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Discussion Starter #12
Ok, will do. Thing is, I don't see a plume following me down the road. But underneath the car is bone dry too and I don't see anything dripping anywhere, no smells really, nothing. The car is in need of an oil change-probably overdue actually. so once i do that I'm going to keep a written record in the car. I will report back with findings afterwards.

In fairness, this thing went to Colorado and was definitively overloaded with gear and people. It started happening on that drive which was all highway. Additionally, I do mostly highway driving at higher speeds (75-80) and I drive nearly every single day a significant amount of miles-almost always well over 100 at least.

I've emailed the PO too in order to find out if that was an issue they were experiencing.

If i need to, I'm comfortable removing the engine and redoing things. I'd like to not, but i also plan to keep this car for many, many years.
 

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Discussion Starter #13
Response from the PO! Seems like a cool person.

Interesting email to see in the in box. I did own the outback for about 2 years I believe, and I bought it used with 90ish thousand miles on it. It burned oil since I bought it. I found out probably much like you when the oil light came on a few months after I bought it. I dove it that way just adding oil every so often. It was slowly getting worse. I also had problems with the exhaust, I think because the excess oil being burned was clogging up the exhaust system. I had to replace the entire catalytic converter system on the car, so that is pretty new. The oil consumption issue along with a failing clutch was why I traded it in last year. Hope this helps in some way and let me know if you have any more questions I could try and help with.
 

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odd that people = dealers etc. replace cats, and don't actually fix the oil consumption / leak.

in subaru OEM parts a federal spec cat for this = $600 and a california / northeast one like $1000.

____

I guess they would have fixed it if it were overheating.

like fixed the head gaskets, after replacing the cat, and it kept overheating.
 

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Discussion Starter #15
Maybe it had been offered and the PO declined? I dunno. Seems to me that if the PO bought it at 90K and then noticed it shortly after, he should've gotten on the horn to the Subie dealer and had it fixed under warranty.

Really wish he would've.
 

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Thought I ran across an extended warranty in the paperwork. But I wonder if I can put some tape over the "1" in my mileage and call Subaru and say I'm a few thousand past the 60K mark...and then I'll need to change the year too.

Gonna go draw up some plans BBL!
 

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Discussion Starter #18
Ok, just changed oil again.

Using Castrol high mileage full synth-no additives (came close to getting a bottle of lucas but I didn't. And yes, I already know what many of you will say about lucas or the other snake oils, no need, it didn't go in) and tracking mileage again as of now. Once the oil light comes on, I will post with the mileage.

Admittedly, I accidentally overfilled by about .2 quarts but I also let it drain for an hour and have it on a mild slope to drain more so I don't think it'll wreck anything. I just want to note this for the oil usage stats that I'm hoping to get.

Stayed with 5W-30 weight for now.

With writing this, I just checked and noticed the rear O2 sensor showed up. Replaced that too. Code was currently off (again, went off after filling up, not sure if it's related, but I'm going to buy a new gas cap too) and I'll post here if it comes on again.
 

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Discussion Starter #19
odd that people = dealers etc. replace cats, and don't actually fix the oil consumption / leak.

in subaru OEM parts a federal spec cat for this = $600 and a california / northeast one like $1000.

____

I guess they would have fixed it if it were overheating.

like fixed the head gaskets, after replacing the cat, and it kept overheating.
Hey eagleeye, nice eye for the P0420.

Ran through a full tank of gas and no codes since the rear O2 has been replaced. I didn't replace the gas cap in order to attempt to isolate possible issues. I'll let you know if it pops back up.

Today I found out some more info about the car-I got in touch with the PO and I called the dealer they purchased it from, used. The car definitely has a new clutch and at 110K, it had the headgaskets done. I can't find if the timing belt was done and now I'm cursing as I imagine it has been but you can never really tell just by looking at it and I really don't want to spend the money on the kit currently even though I know I should just do it for peace of mind.

When the car came back to the dealer, it was low on oil and the guy was reading the write up and it said "tech couldn't turn the motor over by hand". I've no **** idea what occurred. After that, they sent it to auction. And now it sits here. Consuming oil.

Drat.

I'm nearly positive I'll need to pull this motor out at some point and fix this oil consumption issue. I'm looking at splitting the cases for this I imagine, right?
 

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I would think running around with a loose gas cap will give you a evap code for a big leak before anything.

________

the new rear sensor may foul again fast.

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hypothesis: car ran low on oil, they tried to turn the engine by hand via the timing belt, and it turned too slow /hard.

car sold at auction,

subsequent problem with exhaust valves, letting oil get in exhaust. (I wonder if it needs a head or 2 rebuilt).
@idosubaru ideas on this EJ253?
 
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