Q: What might be causing oil to blow out through the exhaust or to burn off? on 1999 Isuzu Rodeo

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I have no noticeable oil leaks, there's never any oil spots under my vehicle on the garage floor. I do find very black splatter behind my vehicle after idling for a time though. I'm going through about a quart of oil every two tanks of fuel, so about 700 miles or so. Gas mileage is good, sometimes great. Is this likely that the piston rings are not sealing well anymore? I have over 300k miles on the vehicle but still in very good condition for that many miles. Have never had a valve adjustment as I have been told that may cause poorer seating rather than better at this point, but I wonder if that could be causing leakage. My spark plugs look like they are burning clean, though a couple looked overly black after 100k miles.
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i bet either the valve seals and/or the rings are worn out. try changing viscosity of your oil to 10-40 to slow down the consumption. at 300k, it is most likely worn out.

Thanks. I did change to Castrol's high mileage 10-40 and that did slow it down a bit I noticed. I run that oil in the summer but switch to 10-30 in the cold winter months because I spend a lot of time in temps below 30 deg, and many mornings down around zero degrees. I was told the lighter viscosity would help starting in cold weather and help the engine warm up faster. Thanks again.