Is it alright to switch back and forth between 5w30 and 10w30? I have a 96' Prelude VTEC that calls for 10w30 (5w30 for under 32 degrees). It has 120,000 miles and gets it's oil changed around once a year because I don't drive it that much. I put even fewer miles than the recommended "severe" OCI each year. I'm currently running Peak Synthetic 10w30 and I have two jugs of PU 10w30 ready to go. I also also have over 60 quarts of Synpower 5w30 for another car that's being used up a lot slower than I anticipated. I was thinking about using up the Synpower 5w30 before using the PU 10w30. I also just picked up two jugs of Maxlife Synthetic 5w30 and was wondering if I should have gotten 10w30 instead. These probably seem like silly questions, but I can't help obsessing over it.