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Cylinder PSI in an Outback?


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21 replies to this topic

#1 gregdavis

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Posted 29 January 2009 - 12:21 AM

I'm looking at buying a 2000 Outback Limited. Because of all the head gasket problems I have been hearing about I had a compression test done to make sure they were good. (did this on a forester and found out the head gasket was bad, saved me a lot of money) They said that the test came back good and that there were no head gasket issues found. I was excited and everything else on the car checked out well. When I got home I looked at the paperwork a little closer. It reads "Did a compression test and found all cylinders between 100 and 115 psi". Does this seam low? Seams like they should all be around 150 psi. Is this a sign of bad rings or valves? I read somewhere that it is no big deal what the psi is as long as they are within 12-14 lbs of each other. Any input would be great, Thanks.

#2 nipper

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Posted 29 January 2009 - 12:35 AM

They should be alot higher then that actually. I would consider that a tired engine. Compresion numbers are not only the PSi but the difference between cylinders. one is a sign of engine wear (similar numbers) the other is usually valves or HG (one number low) and two numbers on the same side high/low a timing belt.

I can't find my manual right now but speaking generally I would expect 175 psi or higher on a subaru engine. On other engines i look at the mileage and make a judgment call.

At that Psi, you should notice a loss of power, maybe hard starting when cold, signs of oil burning.


Maybe its just a mistake on thier part. BTW on a sooby a compression test isnt always conclusive on a bad HG.

the next step would be to do a wet vs dry test to see if the numbers come up, but I tend to doubt the numbers you have more then doubt the engine

#3 gregdavis

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Posted 29 January 2009 - 12:52 AM

Thanks for the feedback. The car has 108,000 miles on it. If the engine is getting tired will it get worse in a hurry? Or will it just have less power and possibly burn a little oil. The car seamed to have plenty of power for what we are used to. Compared to my 95 outback it was fine. The other problem I'm having is putting money into all these tests for a car I don't own. I know that it could potentially save me more in the long run. (it already did with the forester) So I guess the big question is, is this a sign of possible high cost repairs that need to be done?

#4 nipper

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Posted 29 January 2009 - 01:00 AM

When in doubt, walk away.


How did they do the compression tests?


And if those numbers are correct it would need a ring job, which is very unusual for soobies as one of the plusses of the opposed piston is that they dont wear like that normally.


nipper

#5 Gloyale

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Posted 29 January 2009 - 01:27 AM

I would think get another compresion test. their tester may have been off, or had a poorly sealling oring.

#6 frag

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Posted 29 January 2009 - 01:40 PM

Or did the test on a cold engine and did not open the throttle fully.

#7 nipper

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Posted 29 January 2009 - 01:44 PM

Something is not kosher here, i mean at that mileage , its just past puberty for a subaru...

nipper

#8 Snowman

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Posted 29 January 2009 - 02:35 PM

Yeah, that seems really low. I haven't compression tested many subarus to get a baseline reading, but northguy's old 95 legacy with 205k on it made 180 psi on all cylinders. :burnout:

Also, it seems odd that the numbers would be that low while still being consistant between cylinders. Usually they will vary by quite a bit if you're starting to have problems.

I know the EJ cars have problems with voltage drop in the battery cables causing slow cranking speed. Wonder if that would skew the numbers.

BTW, the phase 2 EJ25s (2000 and up) almost never had problems with blowing the HGs internally like the older engines did. They always leaked coolant externally, so even though a compression test is worthwhile, it won't tell you anything about the type of failure these engines are prone to.

#9 OB99W

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Posted 29 January 2009 - 02:36 PM

Something is not kosher here, [...]


I wonder if they did a real (pull the plugs and use a gauge) compression test, or determined it via an engine analyzer. Analyzers use cranking speed to estimate compression --variation in that speed translates fairly well to pressure differences, but absolute compression reading is too dependent on how warm the engine is, battery condition, etc., to be accurate.

#10 nipper

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Posted 29 January 2009 - 02:55 PM

I wonder if they did a real (pull the plugs and use a gauge) compression test, or determined it via an engine analyzer. Analyzers use cranking speed to estimate compression --variation in that speed translates fairly well to pressure differences, but absolute compression reading is too dependent on how warm the engine is, battery condition, etc., to be accurate.



Its been a while, but do they still do it with the engine running. Sun machines would kill a cylinder and analyze the rpm drop to come up with a (pretty good) compression number.

I never liked those that did it on cranking speed, too many variables to give a false number.


nipper

#11 OB99W

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Posted 29 January 2009 - 03:13 PM

I never liked those that did it on cranking speed, too many variables to give a false number.


Another method measures cranking current (amperage) and correlates that with compression for each cylinder, which also has its limitations on accuracy. I still like to pull plugs and take a gauge reading, but there's no question with certain engines, that takes some time.

#12 nipper

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Posted 29 January 2009 - 03:16 PM

Another method measures cranking current (amperage) and correlates that with compression for each cylinder, which also has its limitations on accuracy. I still like to pull plugs and take a gauge reading, but there's no question with certain engines, that takes some time.




That was the driving force behind 100,000 mile plug changes. Some plugs are just impossible to get too. They used the old model that a owner would be selling the car after 3-4 years and would never have to face that repair bill.

Step 1 - remove engine
Step 2 - remove plugs.



nipper

#13 davebugs

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Posted 29 January 2009 - 03:28 PM

I do them with a cold engine and have a good battery in the car and a fully charged powerful jumpbox. This makes sure that the car doesn't crank slower on the last cylinder than the first. Well - it's the best that I can do and by ear they don't seem to start to run down.

I just forget what I usually get on 2.2's.

I must say I've never had to do a compression test on a 2.5 and that could be downright unpleasant!

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#14 OB99W

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Posted 29 January 2009 - 03:42 PM

Step 1 - remove engine
Step 2 - remove plugs.


That reminds me of a bit about some home improvements:
1) Remove roof and temporarily set aside.
2) ...

:)

#15 Petersubaru

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Posted 29 January 2009 - 09:55 PM

My old 1986 1.8L with 210K miles has 155-160 psi across the board..mostly highway driven

#16 gregdavis

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Posted 30 January 2009 - 10:23 AM

Thanks for all the feedback. I talked to the shop yesterday where I had this done and they confirmed that yes the psi should be higher. They are going to do another test for free today and focus more attention on the cylinder psi (engine warm, throttle closed etc). . Last time is seamed they were just trying to confirm that the hg were good and didn't pay attention to the psi because they were all pretty equal. They did do this test with a gauge because they mentioned the spark plugs should be replaced soon. Seams like if the psi numbers stay the same it is a car I should stay away from. I don't notice any decrease in power though. I'll update later.


External hg leaks can only be visually inspected right? Is it obviuos to see?

#17 bulwnkl

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Posted 30 January 2009 - 02:55 PM

Thanks for all the feedback. I talked to the shop yesterday where I had this done and they confirmed that yes the psi should be higher. They are going to do another test for free today and focus more attention on the cylinder psi(engine warm, throttle closed etc). .



Throttle open is the proper procedure. If it was me, even though the compression is fairly even (all cylinders within 10% of each other is generally the limit), I'd probably pass if it's that low. I wouldn't necessarily suppose there's that much engine wear after only 100k. My money would be on carbon deposits in the rings, but I wouldn't place that bet unless I didn't really need the car anyway and it was very, very inexpensive.

#18 Snowman

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Posted 30 January 2009 - 03:56 PM

Thanks for all the feedback. I talked to the shop yesterday where I had this done and they confirmed that yes the psi should be higher. They are going to do another test for free today and focus more attention on the cylinder psi (engine warm, throttle closed etc). . Last time is seamed they were just trying to confirm that the hg were good and didn't pay attention to the psi because they were all pretty equal. They did do this test with a gauge because they mentioned the spark plugs should be replaced soon. Seams like if the psi numbers stay the same it is a car I should stay away from. I don't notice any decrease in power though. I'll update later.


External hg leaks can only be visually inspected right? Is it obviuos to see?


The ones I've seen have been pretty obvious if they're actually leaking already. Typically, you won't see an actual drip, but you'll see green staining where coolant has leaked out.

Check out the condition of the cooling system too. If the coolant looks nasty, or if the car has ever been overheated, stay away because it may very well start leaking in the future if it isn't now.

#19 gregdavis

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Posted 31 January 2009 - 08:38 PM

Here's an update. The same place retested today and found all cylinders between 120 - 130 psi. during the dry test with battery jump box. Wet test was at 180-190. It should be at 156. Would this be just engine wear for 108k miles?

I had my brother drive the car because he has a 2003 obw. He said it had more get up and go then his. Neither one of us notice any decrease in power even at higher rpms or going up hills. It is not a screaming deal but I would say it is a good deal.

I'm curious what folks think of the new numbers.

#20 nipper

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Posted 31 January 2009 - 08:44 PM

i personally dont like the numbers. I think they are still too low for a car that young. They are OK numbers, but not great numbers, i think you can do better.

There should be minimal increase or none between wet and dry numbers. An increase of 60 psi between wet and dry tells me the rings have some wear on them.


nipper

#21 OB99W

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Posted 01 February 2009 - 08:35 AM

Other possible reasons for low dry compression readings are fuel dilution of the oil, or the wrong viscosity oil. Fuel dilution, if sufficient, can often be detected just by smelling the oil on the dipstick. If that's the case, an oil change will usually bring the compression readings up. However, fuel dilution itself is sometimes a sign of bad rings, so any improvement in dry compression with fresh oil might be temporary.

A 50% increase in compression readings from dry to wet concerns me. If the rings are indeed the culprits, at the mileage the car has it would likely point to poor maintenance or abuse. That would make me leery of the car in general. Unless the deal was very good, allowing for a cushion in case significant problems developed later, I'd avoid this particular car.

#22 frag

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Posted 02 February 2009 - 02:30 PM

That reminds me of a bit about some home improvements:
1) Remove roof and temporarily set aside.
2) ...

:)


Or,
1) Remove the car from the radiator cap and set car aside
2) Screw a new car to the cap.
3) Drive.




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