Really weird, took the xterra on a longer run on the highway, After 15 miles the blue smoke stopped and everything looked good. Then on Wednesday the oil light came on, checked and the dipstick showed no oil. Figured I should have topped it up after the blue smoke incidence. Got 4 quarts and put in started engine and in a few minutes all sounded good, light went off. Checked the oil and it was full. Checked it yesterday morning and still looked good. Checked it this morning and the dipstick was dry, showed no oil. Put a quart in and checked again, showed full, started engine let idle for 5 minutes, no smoke, nothing. turned engine off and checked oil, showed full. What is going on?