Originally Posted by rangerlocal

If it's not smoking black, it's not completely burning it. There may be a culmination of things, like valve cover gaskets. Sometimes they leak at the exhaust manifold side, and burn off the oil under the hood and you never see it smoke. Check the PCV too, it could be partially blocked pressurizing the crankcase and making oil ooze out of the seals.

Get a vacuum gauge and hook it up if you have one. It'll tell you the overall condition of your motor just by a quick peek. Compression leakdown test can also reveal worn rings. More than likely, the rings are pretty worn at 250k+, but it's not uncommon for these engines to go well beyond 300k with no problems. Vacuum gauge and compression test will reveal whether you're due for a rebuild.