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2005 Buick LaCrosse V-6 Engine Oil Mystery Leak

We purchased a new LaCrosse CXL in 2005. Its speedometer now shows 90,126 miles. The 5W-30 motor oil has been changed every 3,000 miles with no indication of oil loss until around 65,000 miles, when I began noticing a slight drop in oil level on the dipstick (about 1/4 quart) within the 1st 1,000
miles following the scheduled oil changes. I then added enough oil to bring the oil level back to full. Within the next 1,000 miles, the oil level again shows oil loss of about 1/4 quart. This has continued over the last 4 years. The car is garaged, and I have never seen any sign of an oil leak on the floor. I have also
driven behind the car several times, and have never seen any sign of oil smoke coming out of the exhaust pipe. Both my Buick dealer and oil-change shop manager can offer no explanation as to why this oil leakage problem developed and continues. The oil shop manager says he has other Buick customers with the 3800 V-6 engine that complain about this same problem of engine oil loss.
There have been no mechanical problems with the car and with the exception of the oil “leak” we have been well pleased with the car. Where is the oil
going? Your thoughts are greatly appreciated.

If there are no external leaks on the engine then it’s burning the oil. An engine can leak oil externally without leaving spots on the garage floor so I assume it has been visually inspected for any signs of external leaks.

If it’s burning oil then you won’t see any smoke because the converters are catching it.

Have they not considered the possibility of a PCV valve problem? The PCV is something that is easy and cheap to service and should be done a somewhat regular basis. Unfortunately, it’s often overlooked.

If the PCV is good then about all I can recommend is running a compression test; both dry and wet. A compression or leak down test is not 100% definitive on pointing out piston ring problems but it’s the only test there is. Ideally, you should see compression numbers in the 190 PSI range.

Another potential cause of oil loss is a faulty valve seal, or plural of that. These are not usually a problem unless the engine has been severely overheated, etc and there is no test for valve seals at all.
Hope some of that helps anyway.

You may not like my answer but I don’t see anything wrong with your car. According to your measurements your engine is using about one quart every 4000 miles. On a modern engine any oil usage under onequart every 1000 miles is considered normal and not indicative of any wear or failure.

True, your 3800 engine is an ancient design by today’s standards, but the components and tolerances reflect modern engineering. Piston ring tension has been significantly reduced in engine design to lower friction but may also cause slight oil consumption.

You could try a new PCV valve and o-ring, but bottom line I don’t believe there is anything to correct or repair on your engine.

I bought a new 2005 Buick Lacrosse in July 2005, had the similar issues, it seems to happen only in Summer for the last 2-3 years.

I would not worry to much 1/4 of a qt. every 1k miles is very little. my 00 300m has about 132k miles and uses about a qt about 2.5k to 5k and i change my oil and filter every 5 to 6k miles. i would change the pcv valve and watch what happens and it costs less then $5.00.

Most people would be happy if their vehicle only lose a 1/4 qt per 1000 miles. I think that if you switch to 10w30, you will lose less oil.

You might try a different brand of oil. Instead of going to the oil change shop, either have the dealer or an independent shop do an oil change. I think you should stay with the 5W-30. Some cars use more of one brand than another. I had a 1971 Ford Maverick with the 250 cubic inch 6. It used 1 quart per 1000 miles of Sunoco 10W - 40. When I switched to Valvoline 10W-40 ( I did the switch because Valvoline was on sale at the time for 25 cents a quart), the oil mileage improved to 1 quart every 1350 miles.
If a change in brands don’t make a difference, then don’t worry about it.