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Old 01-03-2011, 09:01 PM   #1
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Default Compression test results, help me...

Need help interpreting these results.

Infiniti G20. Cracked oil pan, engine ran for 30ish seconds with low oil pressure before I could shut it down. Testing compression to see if engine is salvagable or not. Can't warm up engine first (no oil). 40 deg F ambient temp.

Dripped some Rotella synth into each cylinder. Tested with these results:

#1 over 300 psi (maxed gauge)
#2 210 psi
#3 240 psi
#4 240 psi

Now, the variation is bad, but why are the readings so high? I would have expected low readings across all four. Is the engine toast? This is a daily, not a toy, is it worth tossing a new oil pan on, filling it up, and seeing how it runs?
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Old 01-03-2011, 09:24 PM   #2
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Been reading and it seems like you can get abnormally high readings if you put too much oil into the cylinder (as I likely did as I was frickin' cold out there and slopped a bit too much into #1.

Going to let the cylinders drain overnight and then retest tomorrow without adding any more oil and see what I get.

Please post any thoughts or ideas.
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Old 01-03-2011, 09:38 PM   #3
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Too much oil in 1
But even the variation between 2 and 3/4 is not good.

re-test for sure, but I have a feeling the results won't be to your liking
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Old 01-03-2011, 09:43 PM   #4
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Low oil pressure tends to kill bearings and cam lobes, not rings. Open the cam cover and examine the lobes for abnormal wear.

Put oil in it, crank it with the plugs out until the oil pressure light goes away, start it and listen for knock or other abnormal sounds. After idling for a few minutes, remove the oil filter and cut it open, open the pleats, look for metal flakes. You need to cut it open with a tool that's like a can opener so the cutting operation doesn't create flakes. Race machine shops will have the tool, go bring a 6pack of your favorite machine shop guy's favorite beer. If you see none, you likely dodged a bullet. If you like, after 100 miles, send an oil sample in for analysis.

Re: #2. How many miles on this motor? I've "fixed" 8% leakdown in 1 cylinder and oil consumption in a 100k mile Focus motor with a round of AutoRX oil treatment.
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Old 01-03-2011, 09:46 PM   #5
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Was it 30 seconds idling or racing down the freeway? Either way, as long as it was still spinning when you shut it down, it'll be fine. Throw on a new pan and oil change with some 5w30 for a couple hundred miles then change the oil again.

Those comp numbers must be due to the added oil because they're really high. Test them again without adding anymore oil and see what you get. About five cranks of the starter on each one.

Last edited by flounder; 01-03-2011 at 10:59 PM.
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Old 01-03-2011, 10:03 PM   #6
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Quote:
Originally Posted by 18psi View Post
Too much oil in 1
But even the variation between 2 and 3/4 is not good.

re-test for sure, but I have a feeling the results won't be to your liking
Don't say that....let's just hope that the readings are all screwy because of too much oil.

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Originally Posted by JasonC SBB View Post
Low oil pressure tends to kill bearings and cam lobes, not rings. Open the cam cover and examine the lobes for abnormal wear.

Put oil in it, crank it with the plugs out until the oil pressure light goes away, start it and listen for knock or other abnormal sounds. After idling for a few minutes, remove the oil filter and cut it open, open the pleats, look for metal flakes. You need to cut it open with a tool that's like a can opener so the cutting operation doesn't create flakes. Race machine shops will have the tool, go bring a 6pack of your favorite machine shop guy's favorite beer. If you see none, you likely dodged a bullet. If you like, after 100 miles, send an oil sample in for analysis.

Re: #2. How many miles on this motor? I've "fixed" 8% leakdown in 1 cylinder and oil consumption in a 100k mile Focus motor with a round of AutoRX oil treatment.
144k miles on the engine. Can't fill with oil yet as I don't have a new oil pan...not paying $150+ at a parts store for one, so I'm trying to diagnose as much as possible before paying $50 to have a good used one shipped to me.

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Was it 30 seconds idling or racing down the freeway? Either way, as long as it was still spinning when you shut it down, it'll be fine. Throw on a new pan and oil change with some 5w30 for a couple hundred miles then change the oil again.

Those comp numbers must be do to the added oil because they're really high. Test them again without adding anymore oil and see what you get. About five cranks of the starter on each one.
Probably 20 seconds of under 2000 rpms of extremely light load as I rolled onto my street and 10 seconds of idling, no load, as it coasted into my driveway. Definitely still running when I shut it off. The majority of the oil was on my carport floor.

I think you're right about the oil, I was just nervous about cranking the car that long since the car has sat for a couple weeks since it dumped the oil out and I put too much in (and I was in a hurry). Will test tomorrow night without adding any.
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Old 01-03-2011, 10:32 PM   #7
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With the numbers that high, I wouldn't worry about it. Like someone else mentioned, running out of oil won't kill your compression. If it ran fine before , it'll run fine afterward.

Test again after you get a new pan and some oil in it, just don't add any in the bores.

BTW, is that mark donahue in your ava? I did a report on him back in college in one of my automotive classes. I still have "the unfair advantage" lying around here somewhere.
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Old 01-03-2011, 10:37 PM   #8
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Yup, that's Donohue. One of my racing heroes. Didn't have lessons as a gradeschoolers, wasn't racing karts in kindergarten....he bought his own car in his late teens and worked his way to being arguably one of the greatest drivers in the world by the time of his death.

The caption above it is a reference to his request to the Porsche engineers -- they kept tuning for more power, and asking Donohue when it would be enough. His reply -- "When I can spin the tires in top gear at the end of the straight, then we'll have enough power."
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Old 01-03-2011, 10:42 PM   #9
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Agree with Jason. If it was running when you shut it down, it'll run again. New pan, fresh oil, and it will be okay.
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Old 01-03-2011, 11:42 PM   #10
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what's "low oil pressure" anyway? **** my miata idles at 10 psi or less depending on idle speed and temperature outside.
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Old 01-03-2011, 11:54 PM   #11
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Dunno what PSI, just whatever is low enough to trigger the idiot oil light flickering in a 1994 Infiniti G20.
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Old 01-04-2011, 01:19 AM   #12
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I doubt its even wiped a bearing.
For the cost, (less than a car payment) I'd fix it. If it lasts for only a year due to a bearing or cam failure, will you be ahead financially?

As far as rings are concerned, I bought an '86 Mitsu truck that the orig-owner's kid over-heated. The alloy head cracked through the top of the head. Soo, a rebuilt head was in order. A year and a half later the engine started smoking when in de-cel. After about a month of that she wouldn't stay running without 'massaging' the throttle. Compression? 40. On the good cylinder! The cooked rings finally gave way.
Nineteen months of commuting for 1300 dollars. And I still have the truck, which I'm doing a eng swap on this summer. Woo-hoo!
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Old 01-04-2011, 09:11 AM   #13
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Quote:
Originally Posted by mgeoffriau View Post
Dunno what PSI, just whatever is low enough to trigger the idiot oil light flickering in a 1994 Infiniti G20.

That's when I change the oil on my altima (130K)

Hell my prelude has 5 qt capacity and it's down to nearly 2qts at times when i finally change it.
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