how does an intake manifold leak cause oil consumption?
How does this phenomenon occur, ie, what are the physical aspects
that cause passage/burning of engine oil? |
an uneducated geuss would be. that the vacuum created during the intake stroke would draw oil out of the lifter valley into the intake ports through the leaking area around the ports
causing loss of oil. not sure how much this would use but i am only geussing about this. but it makes sence |
Originally Posted by 85blkrose
an uneducated geuss would be. that the vacuum created during the intake stroke would draw oil out of the lifter valley into the intake ports through the leaking area around the ports
causing loss of oil. not sure how much this would use but i am only geussing about this. but it makes sence RACE ON!!! |
my parents were dead wrong when i was younger. i geuss i do have some common sence.lol
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Originally Posted by CFI-EFI
Absolutely! Good guess.
RACE ON!!! |
:iagree: They beat me to it, summer 2003 I lost a bunch of oil and fouled up my rings to the point they needed to be replaced due to oil being sucked up from between the head and the bottom of the intake runner.
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Not trying to steal the thread but,
Is this as much an issue on the LTx or the LSx engines? The intake design changed quite a bit. Did the change alleviate any of this?
Call me curious. |
thanks all, that sure helps explain what i'll be looking at.
symptom: once warmed up a few mins. a billowing cloud of blue smoke out the exhaust occurs when hitting the throttle after being stopped (for at least 20 seconds or so)....this condition clears up almost immediately upon acceleration. i'm losing about 1 qt. oil every 250-300 miles. this whole condition began 500 miles after the engine buildup, I'm at about another 1300 miles since then. maybe bad intake manifold gasket(s), or the manifold itself must have shifted......hmmmmmmm......this will be evaluated and corrected in the next month. i hope the rings aren't trashed, they're brand new! plasma-moly to boot. and yes, i'm using regular dino oil and went thru a 500+ mile break-in period.......however i don't understand how rings could get fouled & ruined from an intake leak :eek: |
GM has a few Bulletins on the subject - particularly for the V6 which seems to have endless failures of the manifold gaskets. They're explanation is that numerous heat cycles (about 25k miles worth)weakens the seal and the intake ports start sucking oil out of the lifter valley. Rarely, with a functioning convertor, is there any smoke from the exhaust, and that's been my experience even though the vehicle was consuming a quart every 800 miles (though I did foul a few plugs). Very little change in gasket materials - the L98 was redesigned for retainers to help hold them in place and I believe the Vortec uses a rubber sealant (like the V6) around the inlets. Correct torque (some need in/lbs) and perfectly flat surfaces are extremely important.
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Originally Posted by VAHROOM
Is this as much an issue on the LTx or the LSx engines? The intake design changed quite a bit. Did the change alleviate any of this?
Call me curious. Other than the lack of cooling passages through the intake the LT1 is exactly the same as the typical SBC so I'd say they could suffer the same problem. I've never actually heard of the problem before though. When I think manifold leak I think of external, not from within the engine. What do ya know, I learned something today. :cheers: |
Before you go much farther it might be worthy to run a compression check before and after a squirt of oil to check ring seal.
On the rebuild were the valve guides replaced, just knerled or untouched? |
Hey Brad, on mine the problem was that my AFR heads were milled down, thus lowering the intake port a bit and I used the cork gasket that goes on the front and rear china wall instead of using only gasket sealer. When I took the cork out, it all seated nicely. With the cork gasket the Miniram was setting up just a bit too high.
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My AFR/TPIS heads are standard fit for L98's and LT1's. The SR intake manifold is only ported at the runners. The heads are brand new.
The oil smoke only occurs once its warmed up, and only after its been stopped at a light, etc. for a good 20+ seconds.....the blue smoke cloud bollows out once, adn then everything "cleans up" almost immediately afterward --- no smoke while on the gas pedal. |
Brad, The intake needs to sit at the same angle as the heads. If either were milled wrong, and the angle is not correct they can leak. We have had this happen a couple of times. They make templates to check this but they are as rare as hens teeth. I always dry run the install and visually check these angles to make sure they at least look spot on. This is not common but can happen. It is usually the result of small machining errors that "stack up" to cause this.Ponder this possibility. John Daly had a problem with his afr combo and solved it by double stacking gaskets. DO NOT DO THIS! Remember I usually have a slow January(work wise) and may be able to pop in if needed. Good luck!
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If you suspect an intake leak from the lifter valley put a vacuum guage on one of the vacuum ports of the intake or look at the scan tool reading at idle for vacuum (only for 90/91 speed density). Your reading swill depnds on the your cam. If you have stock cam, it should read over 20" hg at idle. Unless you have a huge cam with a lot of overlap, a reading of 10-12" hg would indicate a leak.
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Originally Posted by ld85
Hey Brad, on mine the problem was that my AFR heads were milled down, thus lowering the intake port a bit and I used the cork gasket that goes on the front and rear china wall instead of using only gasket sealer.
RACE ON!!! |
thanks all, for the continued insights. sounds like more nasty possibilities. the vacuum at idle is a very healthy 16", i'm running the LPE 219 cam.
i sure hope it isn't an alignment mismatch at the intake/heads interface. double gaskets no good?....i can believe that. if there's an improper alignment, and measurements are impossible, sounds like i'm in for an unsolvable and permanent problem. |
Not impossible. Just clever solutions. I got it all figured out . Even if my terrible possibility come true, we can fix it. No panicing yet. Normal aftermarket bs. Wecome to the modders club! :cheers:
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Ok Pete, consider yourself on duty call in January! I'm sure my "wrench" can handle it, but you may become the new Marcus Welby, MD, free room & board for the weekend....or at least the trusty cell phone....the latest news is that there's a delay again until early-mid Jan ;)....meanwhile more oil keeps getting dumped in :crazy:
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Originally Posted by bradvette
i sure hope it isn't an alignment mismatch at the intake/heads interface. double gaskets no good?....i can believe that.
RACE ON!!! |
CFI, hey thats great info, the kind of stuff thats helpful to many of us on the forum, thanks :thumbs:
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Please help!
Originally Posted by tjwong
(Post 1549049908)
And it could suck a LOT of oil from that area! Beleive I know, it happened to me sometime ago on a big block!
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I see a lot of young people removing the OEM Positive Crankcase Ventilation, and running catch cans, or rocker cover breathers. personally, I don't think I could hack the fumes in the cockpit, with such a set up.
When I put a magnacharger on my LS powered short bed I put a big loop in the pcv hose, plenum stayed clean and oil consumption slowed early LS1 vettes had oil consumption issues do to pcv design later cars 2002.5 to 2004 used a revised pcv routing to combat oil consumption and oil collecting in the plenum |
383TT PM sent.
Since your new..welcome to the Forum. For us to help you there are several things that are important in any posting. 1) Always state the year of your car. The C4 covers 1984 thru 1996. The 84 with throttle body injection (L83 engine), 85 thru 91 the L98 and 92-96 with the LT1-LT4 series engines. 2) Give us as much information about your problem as you can. 3) Pictures are very helpful on some issues. 4) It is often better to start a brand new thread with your problem than to resurrect a eleven year old thread. 5) Learn the search and advanced search functions. 6) Fill out your profile. Name, city, year of car etc......it may help if a form member lives close to you. 7) Can you wrench on your own car? or new to the game? |
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I had this happen when I put some aluminum heads on a well maintained sbc, used oil like crazy. The ports were wet with oil. They do make thicker intake gaskets that help. My problem was my new heads would have worked fine on a zero decked block. Mine was a stock (never decked) block, causing the heads to sit a little further out. I decked the heads & used thin head gaskets. That bought the heads down & closer, it tighten up the angles. This intake angle gauge will help you figure out if you have a mismatch, you shouldn't need it on a stock motor though.
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