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Discussion Starter · #1 · (Edited)
I own a 2007 Buick Lacrosse w/ 3.8 Series III that I purchased in June. It currently has 44k. The only major problem I am having is that it uses 1 qt of oil every 900 miles. No excessive smoking, and no leaking. Any suggestions?
 

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Wow, nice low mileage find!

The concern may be that the good odometer reading makes people ignore some necessary upkeep/maintenance still required after 15yrs and various known items to keep 3800's happy for the long haul. Gaskets compromised on the top-side of the engine may be the culprit (upper/lower intake, valve covers, etc.), causing the oil to be leaked out or drawn into the intake passages slowly over time.

Overall, this would be about $100 in gaskets/fluids/etc. and a weekend of effort at slow pace (afternoon for someone who's done it a bunch).

Another test before cracking any bolts loose would be compression checks, to make sure things are sealed fine in the piston region, still. I'd suspect so, but doesn't hurt to look.

Other, deeper gasket/seal issues could be front and rear cover/seals and oil pan, but that's not typically the primary issue on these, usually.
 

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If that's the case, I'd lean towards my first couple suggestions about the top-end/intake stuff. The updated aluminum lower intake gaskets came out in ~2012, finally giving a solid fix for the integrity of those sealing surfaces. The routing if many things through the upper intake (coolant to TB, intake air, PCV passages, EGR) causes it to also be a source of issues, just slightly less after the aluminum upgrade for Series 3's.

Pick away at the troubleshooting, and let us know what you find. That helps inform our suggestions for other owners as we deal with the various reasons strange things happen as these 3800's get older and older.
 

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Discussion Starter · #6 ·
There's also an inexpensive ,often overlooked cause of oil loss: a stuck open PCV will make the engine burn plenty of oil.
If you've got any doubts about this:
Read: post #13 of How much oil does your series ii 3800 consume? | Buick Forums
Issues with Chevy 3800 | Bob Is The Oil Guy
That was one of the first things I checked, also the easiest. I am going through a quart about every 900 miles. I also read something about a TSB regarding valve seals, but I haven't really researched that yet.
 

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Valve cover gaskets and bolt grommets are an easy and inexpensive item (rear has some stuff like alternator in the way, is all). The valve seals aren't something I hear much about, but you can inspect them while the covers are off
 

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There's also an inexpensive ,often overlooked cause of oil loss: a stuck open PCV will make the engine burn plenty of oil.
If you've got any doubts about this:
Read: post #13 of How much oil does your series ii 3800 consume? | Buick Forums
Issues with Chevy 3800 | Bob Is The Oil Guy
I'll pass this to a friend mechanic! He'll work on this 3800 project after installing the new rotors and tires from 4 Wheelonline this weekend. He'll be chasing this mysterious oil leak.
 

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I'll pass this to a friend mechanic! He'll work on this 3800 project after installing the new rotors and tires from 4 Wheelonline this weekend. He'll be chasing this mysterious oil leak.

Man, these bots just don't know how to keep it in their pants to pass the Turing smell test once they post more than single phrase pleasantries.
 
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