Well, one of my cars has 2 quarts of Pennzoil 5W-30 synth blend, one quart of Pennzoil 15W-40 Long Life and one quart of Quaker State 15W-40 HDX in there right now. Why? These were what I had leftover after cleaning out my stash of Wal-Mart closeout $0.69/quart containers! I figure there's a 10W-35 blend in there now with a little Moly and some other good stuff. It's only going to 3K or so, anyway!