2002 Outback Ltd consuming oil - Help

[PeterP]

I have a 2002 Outback Limited with 116K miles that consumes about 1 quart oil per 1000 miles. This has been going on for about 2 years now. I also replaced the catalytic converter last summer.

 

The check engine light just came on again and the code indicates another catalytic converter replacement in less than a year.

 

From this I assumed that the engine has been burning oil and this clogged the catalytic converter.

 

I also have been using 5w30 oil in it and recently switched to 5w40 to try to reduce oil consumption.

 

Thinking that the rings or valve seals were bad I had my mechanic do a compression test. All 4 cylinders result in 150psi.

 

I'm stumped. Where is the source of the problem? What do I check next?

[idosubaru]

sounds like you know this, but 1 quart per 1,000 miles isn't the end of the world...except for maybe your convertes it appears. it doesn't surprise me that it doesn't "show up" in your compression tests, whether or not anything related to that is the cause. that's just not enough oil loss to point towards significant internal issues.

 

oil consumption (not leaking) is likely to be rings or valve stem seals. not sure if headgaskets can leak oil into an exhaust port, but they can leak oil.

 

that's some low mileage to be having oil consumption. subaru's don't typically do that. mark territory with oil seaping out of valve covers, totally :lol:!, but consuming oil is odd.

 

first thing i'd do is replace the PCV valve and make absolutely certain a Subaru PCV valve is used.

 

if you're still concerned a leak down test may be in order.

 

what's the history of the engine? one owner? previous issues? Head gaskets replaced?

[ccrinc]

What Gary said.

 

Emily

[PeterP]

Thanks for the recommendations. I'll pick up a Subaru PCV valve on Monday when the parts counter re-opens after the holiday weekend.

 

I'm the original owner of the vehicle.

 

At 20K it had a bad belt tensioner that Subaru replaced. Oil and filter (penzoil 5w30) every 3-4K miles. Regularly scheduled maintenance. Timing belt at 105K along with the front main seal and water pump. Clutch at the same time with the rear main seal. Brakes as needed. Catalytic converter a year ago at 106K.

 

Original head gasket.

Edited July 4, 2009 by PeterP

[hankosolder2]

1 quart per 1000 miles consumption should be not enough to kill a catalytic converter. I think you either installed a substandard cat con or have bad 02 sensor(s).

 

I realize this is sort of an apples-and-oranges comparison, but my Honda has a pretty bad oil consumption problem (600 miles per quart) and has had that problem for the past 30K miles-- still on the original cat, gets great mileage and has no check engine lights.

 

+1 on the replacing the PCV.

 

Nathan

[PeterP]

Update:

 

I replaced the PCV valve with a Subaru valve mid-July. The old one appeared ok to me (the ball rattled fine). Oil consumption continued at 1 quart/1K miles.

 

In July I had my mechanic do a compression test. He said all 4 cylinders came in a 150 psi. He also stated that he did not see any obvious oil leaks.

 

I just dropped it off at Subaru. They performed a leakdown test that resulted in cylinders 1&2: 200psi, 3: 195psi, 4: 190psi which was within spec. At least my rings and valve seals are good.

 

The Subaru Tech said that my 2 month old PCV valve was gummed up and replaced it. Could the (still clogged) catalytic converter do this via excessive backpressure?

 

He also said that the head gasket was leaking and the crank and cam seals were leaking. (The crank and cam seals were replaced 1 year ago during the timing belt replacement. ) He recommended pulling the engine and doing a complete reseal to solve the problem. Their quote was $2300 for the job. Is this reasonable?

 

I plan to have them replace the clutch at the same time for an additional 700-1K (depending on if the flywheel is needed).

 

I also need a new catalytic converter + O2 sensors. There are two cats that are replaced as a pair. Cost $1100.

 

So I am a little miffed at my mechanic who did all the work last summer that just now needs to be done again (except for the leaky head gasket). I'm hunting for a local Subaru-specific mechanic who may be able to offer a better price.

Edited September 3, 2009 by PeterP

[nipper]

Your oil leaks probably mean you are using far less oil then you think you are.

 

Have you had a timing belt done on this car yet?

 

Those compression numbers I dont like, but if subaru says the leakdown is good i wont argue.

 

When was the last time the cooling system was serviced, and what brand oil are you using?

 

What oil change intervals do you use?

 

What kind of driving do you do?

[PeterP]

> Your oil leaks probably mean you are using far less oil then you think you are.

 

The reason I think it is burning oil is the new catalytic converter gone bad after one year. Granted it is an aftermarket one...

 

The original one lasted 106K miles. Is that normal?

 

I am hesitant to install another cat unless I am certain that I'm not going to just gum it up again.

 

> Have you had a timing belt done on this car yet?

 

Yes, last summer.

 

> Those compression numbers I dont like, but if subaru says the leakdown is good i wont argue.

 

The 2.5 NA engine has a compression ratio of 10:1. Wouldn't 150 psi be just about right?

 

> When was the last time the cooling system was serviced, and what brand oil are you using?

 

Cooling system, a year ago. Was using penzoil 5W30 until the last oil change 3 months ago. At that point I put in Rotella 5W40 to try to reduce oil consumption.

 

> What oil change intervals do you use?

 

3K

 

> What kind of driving do you do?

 

My (ahem) wife drives fast on the freeway but reasonable on surface streets. Typical Atlanta driver.

[OB99W]

In July I had my mechanic do a compression test. He said all 4 cylinders came in a 150 psi. He also stated that he did not see any obvious oil leaks.

 

I just dropped it off at Subaru. They performed a leakdown test that resulted in cylinders 1&2: 200psi, 3: 195psi, 4: 190psi which was within spec.

Neither of these test results gives me a lot of confidence. The 150 psi your mechanic found is low -- 185 psi is more typical for the engine. The numbers the Subaru dealer reported are possible for compression readings, especially if there's some carbon buildup, but for leak-down they make no sense. Leak-down testing results are given in a percentage, not in psi.

 

 

At least my rings and valve seals are good.

Compression and leak-down tests can give an indication of ring condition and how well valves seal to their seats, but they don't reveal the performance of valve stem seals.

 

 

The Subaru Tech said that my 2 month old PCV valve was gummed up and replaced it. Could the (still clogged) catalytic converter do this via excessive backpressure?

If the two-month-old PCV valve was more gummed than the much older one which you previously replaced, it might have more to do with the change you made in oil than anything else.

[OB99W]

The 2.5 NA engine has a compression ratio of 10:1. Wouldn't 150 psi be just about right?

If one were to assume 14.7 psi sea level atmospheric pressure and 10:1 compression, it might make logical sense that the result would be 147 psi of cylinder pressure at TDC. However, there are several factors that influence the actual cylinder compression pressure -- two of them are valve timing and expansion of gases when heated (due to compression). Each engine design will vary, but a rough rule of thumb for estimating cylinder compression pressure is to multiply the compression ratio by 18. For a 10:1 design, that would suggest 180 psi as an approximation.

[PeterP]

Here is exactly what is written on my service bill.

 

MISC TECH 1088 PERFORMED COMPRESSION/LEAK DOWN

TEST-CYL 1&2=200LBS,CYL 3=195LB,CYL

4=190LB//LEAKDOWN 5%-ALL TEST WITHIN SPEC

1088 C

 

Considering what I've recently learned I wonder if my mechanic did the compression test on a cold engine. Or if his tech just decided to sit in the car and eat lunch instead. Sigh.

 

Thanks for the expertise you guys have offered.

[nipper]

Compression should be 180-185 PSI. I would have a proper dry/wet compression test done first to see what the numbers are. If you want a vacume gauge can tell us the condition of the engine too.

 

 

The aftermarket Cat, if it was an Eastern Cat, I would fault the cat and not the engine. A Cat can tolerate a fairly large amount of oil burning, as cars consume oil in thier normal operation.

 

First thing first, get a proper compression test.

 

 

nipper

[OB99W]

Here is exactly what is written on my service bill.

 

MISC TECH 1088 PERFORMED COMPRESSION/LEAK DOWN

TEST-CYL 1&2=200LBS,CYL 3=195LB,CYL

4=190LB//LEAKDOWN 5%-ALL TEST WITHIN SPEC

1088 C

That's clearer, and those numbers are reasonable.

 

 

Considering what I've recently learned I wonder if my mechanic did the compression test on a cold engine. Or if his tech just decided to sit in the car and eat lunch instead. Sigh.

Unfortunately, I suspect something closer to the latter. Even if the readings were low due to cold engine (or throttle not held open, etc.), I'd still expect some variation from cylinder to cylinder (as Subaru determined). The ''150 psi'' reading for all cylinders is suspect.