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I've only had my 09 Tribeca for about 1 1/2 years and don't know much about its history other then it had one owner from Quebec. I've been getting full synthetic oil changes every 5000km since I got it (usually 3-4 months) at the Delta Sonic in Niagara Falls NY because of the lower prices on synthetic changes in the States. I'm usually down about 1 - 1.5 litres at the time of each change, its been that way since I've put the synthetic in when I got the vehicle.
About 2 months ago my CEL came on, went off about a week later for a couple days, then came back on again. I took it to the dealership and they replaced both Catalytic Converters under the 8year/130000km factory warranty that comes with the vehicles in Canada. When I picked up my vehicle the dealer said that they will not warranty these replacement cats because the engine is leaking oil internally and will eventually cause these cats to fail as well. They recommended a small block rebuild starting at $7200 which I am not willing to sink into this vehicle. I'm skeptical and think they may just be trying to recoup some of the cost of the work they did. When I got the vehicle back I put in an oil treatment that said it would help stop leaks and condition seals. About a week after that I got my emissions test done and the car past with flying colours, my CEL has not come back on over the last 2 months either.
I've read that switching to conventional 10w40 may lower the amount of oil that I'm losing? I have no oil leaks that I can see on my driveway, and I see no puff of smoke when I start my vehicle (although the Subaru Techs said they saw one after they replaced the cats even though they only had the car for half a day), even when it's sat for 3 or 4 days. I've read other members comment that if oil is leaking inside the motor, then Rotella could contribute to the cats failing as it deactivates the cats...so I will definitely stay away from that. I was also told at the dealership that I have a leak at the timing chain cover and around the oil pump lines but that I will not see oil on my driveway from those leak points because it will burn off the motor before it hits the ground. The oil stabilizer I put in seems to have helped in some way as I have not seen my oil drop at all in the last month. What would the oil experts recommend my doing to help keep this vehicle running as long as possible? I have 2 years until my next emissions test needs to be done, and they won't look at the vehicle if there's a CEL on. I'm hoping I can fix the external leaks, or have a mechanic do it, but I really don't want to sink too much money into ripping the whole engine apart...
 

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"the engine is leaking oil internally and will eventually cause these cats to fail" seems like a fancy way of saying you've got a blown head gasket, in which case, a small block rebuild isn't necessary, and the fix should cost less than half what you were quoted.

Switching to conventional oil will only slow/stop an external leak, i.e. from the timing chamber. However, a timing chamber leak will be quite evident on the ground eventually (or on the inside of the under cover)... that will not burn off on the motor.

What was the CEL code? Guessing it was probably a P0420, in which case, I hope it was actually the cats and not one of the many other half dozen causes.
 

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First - the dealer doesn't eat the cost of warranty work, although it is billed at a lower rate to Subaru of Canada who does eat that cost.

2nd - I assume they said that oil killed the cats because they actually saw oil in the exhaust pipe that was unusually high quantity.

In which case, there is a good chance what they said is true.

However, there are plenty of 'know it alls' who simply say what they THINK is right without actually knowing it is right. It is very common for P0420 to result in dealer swapping in cats without actually troubleshooting any of the other causes as Psygnal points out.

I would a) get a 2nd opinion, b) ignore it and deal with it when the check engine light comes on or c) diagnose the original issue with the P0420.

Burning that much oil is fairly common for our H6 engine. I think b) is your best course of action if you have the mental ability to do that. It's cheaper to replace cats every 4 years than fix the engine honestly. c) is the best path, but might be impossible now that you have new cats. a) will give you good piece of mind and a reasonable intermediate path on the oil burning issue.
 

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Discussion Starter #5
I think I'm gonna switch oils to conventional instead of synthetic, going with a thicker 10W40 oil and potentially keep adding the oil additive since it's been doing a good job at keeping my oil levels up. This "problem" with the motor may have been there for years causing a small oil leak to gum up the carbs over the 115,000 km life of the motor, or it may have happened only in the last couple thousand kms since I've owned it, I have no way of telling. I find it odd that they'd warranty the cats, but not stand behind the motor that caused the cats to fail. If I was to try and trade it in to a non-Subaru lot towards another vehicle is there any easy way to fix the external leaks they've noted around the oil pump and timing chain cover, are these issues worth fixing without tearing down the motor to get at them, or just leave everything as is?
 

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The diagnosis (which implies worn piston rings) seems much less likely than oil consumption due to cylinder head or head gasket issue. Although the latter is possible most people with leaking head gaskets experience overhearing problems rather than oil consumption. I would suggest that worn valve stem seals are the most common cause of these engines burning oil. This would require a cylinder head rebuild which will still be expensive but less than an engine block rebuild.
 

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With this kind of money at stake, there needs to be at least some semblance of good-faith diagnostic effort, such as, for example, ruling out a malfunctioning PCV circuit.
 

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It is very common for P0420 to result in dealer swapping in cats without actually troubleshooting any of the other causes as Psygnal points out.
Extremely true. I've had shops tell me before that an oxygen sensor failure is "extremely unlikely" and I should just replace my cats.

Let's see...one part costs $50-60 and the other costs $600+. Which am I going to replace first?

Btw - the instance I had with this code was on my Forester - I replaced the sensor with a direct replacement Denso (OEM manufacturer) for less than $55 and the code never came back. The cats were fine.

It's also worth just looking at the wiring for the o2 sensor before you order anything as it could just be mice chewing through the wiring.
 

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Even better yet, looking at sensor data to verify performance. A good tech, as explained in CarDoc's excellent thread over in subaruoutback.org can directly identify the issue causing P0420.

http://www.subaruoutback.org/forums/66-problems-maintenance/49537-p0420-diagnosis.html

Then there is the "$5 anti-fouler solution" which involves putting a spacer in between the O2 sensor and the exhaust. This will keep the code from coming up but is only masking the main issue.
 

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Discussion Starter #14
Now that the cats have been replaced under warranty, I'm curious as to what other issues could have caused their failure, would they have saved the info from the computer other then the error code, and openly give it to me if requested? Techs said the cats had oil in them which caused their failure, but I didn't see them, and thought that 1-1.5 litres of oil being used was concerning at first but was typical after reading everyones comments on this site. Before their replacement, I was questioned about the gas I use in my car, they said they saw some pinging codes(?) which could indicate that I was using cheap gas and they told me I should only be putting premium in this engine. I told them that according to the manual this was wrong, and part of the reason I bought the newer vehicle over the old one was because I was able to use any gas I wanted. My Infiniti G35 recommended Premium fuel but seldom saw it, and I never had any problems with it. 85% of the time I fill up with gas its at DeltaSonic (can't beat a carwash and hand dry for only $5, and another 3cents off a gallon when the carwash is purchased), the other 10% usually at TOPS. Are either of these particularly "cheap gas" that would contribute to the "pinging"? The other 5% of the time I fill up with gas in Canada is usually at Esso, Shell, or Sunoco, although there is a new GULF gas station opened up around the corner that I will probably use occasionally out of convenience. Any likelihood of gas from any of these stations somehow contributing to my CAT failures? It's been a month now since I put the oil treatment in and my levels have not dropped at all, also I have not seen an overheating issue since I bought the vehicle, I get the first 3 little bars just under halfway on my temp gauge after about 10-15 minutes of warming up/driving in the winter, which I've always gotten to and that's as far as it goes...
 

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Cheap gas is one of two things:

Lower octane : no issues for an 09, but 06-07 should run premium
No detergents: This is real, and I don't recognize several of the brands, but generally if you are buy 'discount' gas you should put a bottle of fuel injector cleaner in your tank every oil change.

Neither will give your cats issues, but will cause carbon build up and/or pinging which will reduce power.

You should have put premium in the G35 for maximum fun. Modern cars will pull timing and run rich if you are on low octane which is just sad for a fun car like the G35.

I consider replacing both 02 sensors if you want to go above and beyond.
 

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Well, first off your dealer is wrong about the gas - the EZ30 found on the 06-07 Tribeca recommended premium fuel (and it was worth it for the performance & fuel economy), but it was not required. The EZ36 on the 08+ Tribeca is 87 only. Putting premium in it would be a waste of money.

I don't know anything about the gas brands in Canada - do you guys have a "top tier fuel" program like we do in the States? I would look for some sort of certification that considers fuel to be higher standard if you're worried about it.
 
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