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1998 Buick Lesabre Excessive Oil Consumption

Tiny
444FIRE
  • MEMBER
  • 1998 BUICK LESABRE
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 62,000 MILES
Guys - No one can figure out why my professionally rebuilt engine uses a quart of oil every 800 miles. The upper plastic intake manifold interior is coated with oil every time it's taken apart for inspection.

No smoking, no oil staining on the rear bumper, tailpipe is clean and the engine runs smooth.

The only portal between the crankcase and the intake manifold is the PCV system I am told. The PCV has been replaced 6 times. It is always wet on the "dry" side when inspected.

The bolts sealing the aluminum intake manifold to the engine block have been confirmed as sealed using a solvent test.

Where do we go from here to eliminate the oil consumption?
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Thursday, January 29th, 2009 AT 9:53 AM

27 Replies

Tiny
RACEFAN966
  • MECHANIC
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You said the upper intake is coated so there is either a crack in that upper intake clean it and look it over very carefull and check the lower intake and gasket to it being on wrong or something. If you are using that much oil it should be smoking like crazy. How was the engine rebiult? Meaning was it just a rering job or was the block bored and honed and new pistons and rings and etc. Let me know what you can and we will take it from there. Also check to make sure that the metal oil sheild in the intake is not missing.
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Thursday, January 29th, 2009 AT 10:27 AM
Tiny
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ALL INTERNAL COMPONENTS ARE NEW. THE MACHINE SHOP TELLS ME SINCE THIS ISN'T A "SMALL BLOCK" CHEVY ENGINE, IT'S A V-6 3.8, A METAL OIL SHIELD IS NOT USED. CAN YOU CONFIRM IT IS REQUIRED BY SHOWING A SCHEMATIC OF IT IN AN ASSEMBLY TYPE DRAWING? THANKS.
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Thursday, January 29th, 2009 AT 3:19 PM
Tiny
RACEFAN966
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Ok the shield they are refering to is the shield for the EGR passages in the front of the upper intake where the exhaust crossover is and such. You are sure that the the gaskets for the intake upper and lower are on correctly and didn't slip during installing?
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Friday, January 30th, 2009 AT 10:37 AM
Tiny
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The shield is in place - the tech working on it questioned how the EGR would permit ooil entry -
The gaskets have never been found to be out of alilgnment during the many, many tear down inspections (6-8 times?) And the engine idles smooth and runs like a top.
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Friday, January 30th, 2009 AT 12:01 PM
Tiny
RACEFAN966
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Ok good have the plugs been pulled to see if any are building any soot? Does the intake have any cracks upper or lower? As for the EGR it will not allow oil into the intake.
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Friday, January 30th, 2009 AT 10:51 PM
Tiny
444FIRE
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We are now using the second GM factory upper intake assembly, just to be sure we're not missing a hairline fracture. There is no fouling on any of the plugs. The lower intake assembly was filled with laquer thinner, left overnight, and found to be at the same level in the AM. We are on our 6th PCV valve.

Is it possible that the crankcase is creating too much pressure and forcing the oil up, rather than vacum drawing it up? Thanks.
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Saturday, January 31st, 2009 AT 7:07 AM
Tiny
RACEFAN966
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How much vacuum does the engine have? Is the breather side of the system clean and doing its job. Have checked the compression to make sure that is all level and at the proper. If by chance the compression rings have the gaps lined up then you will get a lot of crankcase pressure. This is why I put them at 10 and 2 and the oil rings at 4, 8, 6 oclock. I would do a compression test just to make sure where it stands.
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Saturday, January 31st, 2009 AT 8:52 AM
Tiny
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A leak down check has been done twice with passing results - vacuum runs around "19". New air filter. All rebuilding and trouble-shooting is, and has been performed by a machine shop that has assigned their two best 30+ year experienced techs to this repair. They're stupified at this point. I shared that to let you know that in their opinion, no stone has been left unturned. Clean plugs, no smoke, runs like a top @ idle and hiway speeds, no oil residue at the tailpipe, yet gets only 800 miles to a quart of oil. An absolute mind bender for sure!
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Saturday, January 31st, 2009 AT 9:05 AM
Tiny
RACEFAN966
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It still don't mean the compression rings haven't turn. So what was the compression numbers? I am an engine specialist (performance engines to be exact) and have been schooled in this field and been doing it more then 25 yrs I am only trying to help as there is no other reason if all else is good that the crankcase could be loading up with pressure.
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Saturday, January 31st, 2009 AT 9:09 AM
Tiny
DOUGANDLAURA
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Hi there. I have a 99 Buick Lesabre and just went thru something very similiar. After having lots of work done, I still had the same problem. Turns out the upper air intake on our engines are notorious for this problem: the EGR stovepipe is made of plastic and eventually (on mine, it was at 115,000 miles) it deteriates to the point there is a hole in there. Very hard to find if you don't know it's there. You have to stick a screwdriver up inside of that hole to feel it. Anyways, you can get an aftermarket upper intake manifold. Waaaay cheaper than GM's. Problem fixed. I can't say for certain that this is your problem too, but upon research I found out that on this particular design, it's not an "if". It's a "when".
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Saturday, January 31st, 2009 AT 2:31 PM
Tiny
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Whoa! Please accept my apology if I offended you, or gave you an impression I was questioning your abilities. Sorry. I was only offering up a little background for your reference. We are certainly looking for someone to help us solve this problem once and for all.

I don't know if a compression test was done. The shop only refers to a "leak down" check. I'll ask about a test being done Monday. Thanks for your input. It's appreciated.
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Sunday, February 1st, 2009 AT 7:04 AM
Tiny
444FIRE
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Thanks for the input. All of my components are new because of the EGR stovepipe failure. Dan
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Monday, February 2nd, 2009 AT 7:30 AM
Tiny
RACEFAN966
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Not affended just explaining that I do have some years in the field incase you thought you were talking to a shade tree mechanic thats all so no worries. Did you find out if they did a compression test or not? If so let me know what was found with numbers ok. Thanks and sorry if I sounded like I was upset. Get back to me ok. Thanks.
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Monday, February 2nd, 2009 AT 12:41 PM
Tiny
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I was told that both the leak down test results and the compression test results were within tolerances. They didn't have the exact numbers in front of them when I called to ask. We're standing still scratching our collective heads, not sure where to check next. Thanks.
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Tuesday, February 3rd, 2009 AT 7:02 AM
Tiny
RACEFAN966
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I still believe that the compression rings in one or more cylinders have lined up there gaps or the cylinders may not have been bored so one is out of round.
Can you tell me if the block was bored or just honed and what rings were used ie-molly or cast. Was your old engine rebuilt or was it a reman engine from a builder?
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Tuesday, February 3rd, 2009 AT 10:00 AM
Tiny
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The original block was bored and fitted with new pistons and rings. Today they are removing the lower intake manifold. The manifold area was filled with solvent (laquer thinner) last night and was nearly gone this AM. The shop techs are thinkng there's a porosity problem. I'll let you know what they learn after doing a solvent test on the bench to locate the area that's weeping through. Thanks.
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Tuesday, February 3rd, 2009 AT 1:28 PM
Tiny
RACEFAN966
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Ok do that as this is very puzzling for me as well. I hope it is just an intake or something like that.
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Wednesday, February 4th, 2009 AT 9:56 AM
Tiny
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The intake component was removed and filled with solvent overnight. The solvent was gone in the AM but no signs of leaking through the non-ferrous material. It must have evaporated?

I llike your theory about pressure in the crankcase vs. Vacuum. The repair techs dispute the theory due to the results of the compression and leak down tests. Can over-pressurization occur even though the cylinders pass the tests? If so, how can I explain it to the techs? Thanks.
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Wednesday, February 4th, 2009 AT 10:37 AM
Tiny
RACEFAN966
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As an engine builder myself as well as lots of schooling on cars it is not impossible. The oil is coming from somewhere and if it in the pcv system and not able to rid it self of all the crankcase pressure then the intake fills with it there fore using oil. I am not saying that they don't know what they are doing I am just saying that this can be a possible cause. See you have three ring pistons a top compression ring and second compression ring and three piece oil ring at the bottom. They have gaps and if the compression ring gaps happen to have lined up or come to close to lining up then you will get excessive crankcase pressure and it will be relieved through the pcv system. Is there any oil in the air filter area too?
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Wednesday, February 4th, 2009 AT 10:48 AM
Tiny
444FIRE
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No oil in the air filter system. I understand the piston rings. What I'm not able to understand is if the ring gaps line up, wouldn't they create an unsealed cylinder condition? The loss of compression should show on the compression test, which it doesn't. The techs are willing to pull the engine and take a peek, but their ABC's of compression knowledge indicate they need to look elsewhere first. Only, they don't know where to look next. Your continued interest in resolving my problem is appreciated. I hope you hang in there with us.
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Wednesday, February 4th, 2009 AT 11:41 AM

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