Buick 3.8 uses 2 quarts of oil between changes

I'd guess that it is burning it. While it may seem high, a quart every 1000 miles is still the accepted mark for "normal" consumption. Given how much it is using, I'd save money and use regular, not high priced synthetic. Sure, it is better, but you can't prove it by your engine.

FWIW, my last GM 3.8 had 125,000 miles and the oil was changed every

7500 miles. Only once did I have to add oil between changes.

You won't see any smoke if the cat is working right. Its unlikely the metal is absorbing all the oil.

My 3.3 (same basic engine as the 3.8) went 250k. O&F every ~7500. Rarely had to add oil. The engine was still great but the rest of the car wore out.

You won't see any smoke even without a converter until an engine is burning oil faster then a quart every 500 miles based on my experience with a GM 350 that burned a quart every 500 miles since the time I bought it at 24K miles till I sold it at 120K miles. The whole time I owned it I never saw even a puff of smoke and it had zero leaks.

At first I was thinking "2 quarts between oil changes, that's pretty bad." Then I see it's 6000 miles, and think some more. I used to change oil at 2500, and most my cars burned 1/2 to a full quart, especially if I was running a lot of high speed. My 2 350's weren't any different. A quart every 500 would bug me, and I had a Ford PU with a 352 that did that, except more like 300 miles. Bugged me bad. Especially since I personally rebuilt that engine except for having a speed shop do the micrometer work and give me bearing and ring sizes to use, and do the block bath. And I had a head shop do the heads. They f***ed up on the valve seals, and it sucked oil at high vacuum. Did a 2000 mile road trip and it used less than 1/2 quart. But around the city in stop-and-go, it just sucked in the oil. As you say though, it didn't smoke. No cat. So 2 quarts every 6000 isn't anything I'd worry about. Not much anyway, especially if I was running it at +70 mph a lot.

And the typical person who never checks there oil and changes it every

3000 to 6000 miles would never even know it's using any oil since even at 2 quarts low the oil light would never come on. In my Blazer it would get as low as 2 quarts before the gauge would start to show low. Most of the time I noticed it on a longer trip at high speed, it would start to have a lot of oil "up top" in circulation and then the lifters would start to starve for oil and get noisy. So I'd slow down for the next 50 miles till I hit a gas station and could put more oil in.

Of course, all the "extra" oil in the pan is just for going up very steep hills and turning sharply.....and to make it seem clean longer.

On that radio show "Car Talk" a few years back, one of the guys had some old beater that required the same amount of oil added, per miles, as a car that burned no oil that had normal oil changes....so he never had to change the oil. Perfect! (Unless you care about the planet, or need to pass emissions. Nothing worse than a VW bus with a "save the planet" bumper sticker, billowing black smoke as it drives down the road)

GW