We have a new-to-us '05 xc70 with about 173K miles on it. On a recent 500 mile round trip, a weird oil loss occurred. I checked the oil before leaving, and it was full. When I arrived at my destination (250 miles of mixed highway and interstate driving, mostly between 45-75 mph) and let the car sit overnight, it was about 1 quart low. I drove home, guessing that it would be a quart low when I arrived, but there appears to have been no oil loss on the return trip, though I took the same route and drove at similar speeds and in similar traffic. I'm baffled.