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

Absolutely! Good guess.

RACE ON!!!

my parents were dead wrong when i was younger. i geuss i do have some common sence.lol

And it could suck a LOT of oil from that area! Beleive I know, it happened to me sometime ago on a big block!

: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.

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.

It's absolutely not a problem on the LS1 engine. The lifter valley on these engines is not exposed at all by removing the intake, so there's no worry there.

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.

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!

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.

This can be a problem whether you use end gaskets or not. If the block is decked and/or the heads are milled, every point on the head, above the deck is lowered down the "Vee" (of the V8 shape). That forces the manifold to ride up higher in the "Vee" relative to the heads and cause port, and in severe cases, even bolt hole, alignment problems. The machine shops have charts to tell them how much to take off of the manifold gasket surface, and even the bottom of the manifold, for a given amount of surface milling. A sneaky problem can pop up, when the block is done in one session and then you go back a month or two later and have the heads done. If they don't know you well and put two and two together, the problem may not come to light until you're wishing for thinner manifold gaskets, so you can get the bolts started. I know many are aware of this, just a reminder.

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:

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:

Double gaskets would aggravate the misalignment due to excessive milling. As the block is decked and/or the heads milled, the ports become lower in the "V" than designed. As they are moved down the "V", closer to the apex, the heads become closer to one another. Therefore, the fixed width manifold rides higher up in the "V", where the ports USED to be. This can expose the bottom of the ports in the heads to the valley, or at least allow less common surface for the gasket. A thicker, or more gaskets, raise the manifold even higher, where it is already too high. The solution is to mill the intake manifold gasket surface of the heads or of the manifold, so the manifold can drop down to it's proper position. The problem with milling the manifold, is that you end up with a "matched" set of heads/manifold. The heads won't take any other manifold, unless it's similarly surfaced, and the manifold won't work with with any normal heads.

RACE ON!!!