Whenever I have tried extending oil change intervals with Mobil 1, or even with regular oil, I find that oil consumption goes up. For instance, if my car burned 1 quart in 3000 miles, (when I used to change it), then the next quart would be required in about another 1000 miles. I take this to mean that either some of the additives are exhausted, or fuel dilution is increasing consumption, or? It then seems to require another quart every 1000 miles or so. I have changed viscosities, etc., trying a heavier oil, but in general oil consumption goes up. The latest car I tried this on was a 2001 Honda Oddyssey. It isn't low at 3000 miles, but it begins to drop below full at 4000, and it is a quart low at 4500. After that it will be a quart low within another 2000 miles. Comments?