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This is crazy, but Oil Burn? The Story of conquering phantoms.

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This is crazy, but Oil Burn? The Story of conquering phantoms.

 
Old 09-24-2018, 01:52 PM
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Ok so, this is going to sound crazy as it all happened on whim.

Some of you know, I purchased a high mileage car. The car had been well maintained, and cleaned, however it sat for 3 years with seldom driving in a garage. It wasn't until I started driving it ALOT, as well as wrenching to clean and replace some parts that the oil consumption went up... Alot.

I was seeing extremely high rates of consumption the harder I drove. Which will all make sense in a second, I hope

So I replaced basically every rubber gasket on the top end I could think of, fixed new oil leaks from faulty replacement gaskets, and old gaskets that started being heat cycled again and we're now leaking. I went down the road of it could be the PCV, or Valve Stem seals, or rings... Etc...

But wet compression tests are perfect, leakdown in 6-8% range. I had, in my head, knocked rings of the list of possibilities for the most part. My next guesses, we're the PCV system. But throttle body and intake manift are clean as a whistle, and the PCV and hose are new.

So now(at the time) I am sitting here, drinking and staring at the car in the garage, I've detailed the engine bay and under the car, clayed the subframe, removed part of the engine bay accessories to clean the paint, and over the course of the past month, degreased the engine 4 times to verify no external leaks. I did the valve seals, without change to consumption.

So here I am, sometimes burning 2/5 upto 1qt per 1000 miles. Again degreased the engine, took it for a 5 minute spin, and notice "seepage" around the oil filler.

Now for the interesting part. I turn the car on, and put a stethoscope by the filler plug and hear air. I thought for a moment, the oil filler cannot attribute my oil loss, with no oil on the ground. What I didn't think about, is that this air leak, is a vacuum leak, and the crankcase at low RPM will always have positive pressure, and not under enough of a vacuum to seat the rings and minimize blowby.

Replaced the Oil cap gasket, fixed the vacuum leak, old gasket would bounce around +2 to -3hg crankcase pressure at idle, with the new gasket, it's holding at -12 to -14hg. It's been two gas tanks, and 650 miles of driving like an asshat pedal to the metal. Dip Stick still on full, my tail pipes are no longer fully sooted after a tank.


Tl:dr
In short, if you have an AP1 and your shit is old(they all are old now!), And you cannot figure out your oil consumption, and tests are giving good numbers/results. Do yourself a favor, and test crankcase holding pressure/vacuum, find the air/vacuum leak, and your rings may seat properly and reduce your consumption.

Hope this helps someone, and they don't give up, as my story is about a motor with 220k+ on it, now with unmeasurable consumption rates. The End

Last edited by Deckoz; 12-31-2018 at 08:57 PM.
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Old 09-24-2018, 03:33 PM
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How have you meassured the crankcase pressure?
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Old 09-24-2018, 04:03 PM
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burning 2/5ths of a quart per 1000 miles is quite good of a burn rate for these motors, I don't think you can expect less than that. Even at the top end of 1 quart per 1000 miles you are still not near the point of condemning the engine or it's parts. Perhaps for other modern engines that would be a very high consumption rate, but not for these engines. If the engine runs good, it has good compression and leak down, and you don't have smoke coming out the tail pipe then you are doing as good as one can expect. I wouldn't stress over it.
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Old 09-24-2018, 07:26 PM
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That is totally awesome! I imagine this will help a lot of people. You may have opened up something very special!

Not sure why this isn't getting more attention and praise...
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Old 09-26-2018, 05:33 AM
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Excellent bit of trouble shooting. I always admire people that can logically narrow it down and discover the true source among many possibilities.
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Old 09-26-2018, 12:51 PM
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After some cap problems =
1 undone itself on a replacement engine<found it on top of gearbox>a vibration that took a while to find !!
found it and replaced again<was using type R cap from another car>
2. I over tightened it and cracked the thread area.<after some miles>oil every where..
Then found out No cap gasket fitted on the replacement engine supplied prob fell of at service some miles ago.
Both times a little noticeable decrease in power,maybe timing advance/retard because no vac/ psi.
Have now drilled the cap and have it zip tied
= So maybe add, Check ignition timing advance also to the list.?
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Old 09-26-2018, 05:16 PM
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Most are likely in disbelief of the simple solution. Your cap wasn't missing the gasket was it?
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Old 10-02-2018, 10:20 PM
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Going to have try this -- just checked my cap and it looks like theres a non-oem gasket on there. Maybe this will help with my oil consumption on my MY00.
Will report back.
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Old 10-03-2018, 01:06 PM
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...yeah, but if you have significant oip consumption, and you notice or suspect an issue with your oil cap gasket, then there is no harm in addressing that first and just seeing if it addresses the excessive oil consumption, without having to go through the not insignificant effort of measuring crankcase vacuum, then proceeding to try and track down any leaks.

Low hanging fruit.
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Old 10-03-2018, 08:57 PM
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Originally Posted by Car Analogy View Post
...yeah, but if you have significant oip consumption, and you notice or suspect an issue with your oil cap gasket, then there is no harm in addressing that first and just seeing if it addresses the excessive oil consumption, without having to go through the not insignificant effort of measuring crankcase vacuum, then proceeding to try and track down any leaks.

Low hanging fruit.
Yup, something cheap and easy to do first. No harm in replacing a 18 year old gasket.
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