I change my
oil about once a year and that's about 5000 miles. I use Royal Purple and a K&N filter that costs me about $10. I've got over 25,000 miles on the engine and they have not been all that gentle, but then, its a Chebby and is inherently able to withstand neglect and abuse. I've never had the
oil analyzed but when I do change it, I can barely hold on to the filter when I slop
oil down the sides of it. Very scientific reasoning that the oil is still plenty slippery. ha.