Where is the oil going?

I have a 1999 Bonneville with 49,000 actual miles - a year or so ago it started using 1-1 1/2 qts of oil between oil changes (3,00 miles) . No visible leaks, no blue smoke in the exhaust, plugs show no sign of burning oil - have replaced pan gasket and upper and lower intake gaskets. Still does it - where could it be going ?

Run your finger around the inside of the exhaust pipe and see if you get any oily/sooty residue. Also check your coolant to see if it has any oil in it. That would be the places I would check if I didn’t have any puddles under my car.

You could still be burning it, just not enough to be seen as smoke. BTW, this is considered acceptable by most manufacturers, although I would disagree. I burn a tad more than that with my '88 Supra, 240K miles on it. I use about 1 quart every 1000 miles, but do not see smoke. I know I’m not leaking it, because there are no spots or drips since I replaced the rear main bearing seal 3 months ago.

I assume that is 3,000 miles between changes. 1 - 1? quarts usage is not more than the manufacturer considers acceptable. It is likely being burned and the converter is eating it. The converters can only handle so much before they are damaged and that is usually at a higher rate than you are now at.

Yea I agree that I believe it is higher than I would like and it is higher than any car I have owned, but that is life.