5,000 mile service coming up this weekend and I've only got 4 qts of Havoline 5w-20 but I need 4.5 qts for a complete service. I have half a quart of Mobil Drive Clean Plus High Mileage Syn Blend in 10w-30 (GF3/SL rated) and was wondering if I could use that as the final half quart. Normally I would just get some more 5w-20 Havoline but since I've got a stash of M1 0w-20 waiting in the wings, I really don't feel like having the extra motor oil sitting around. Anyone see any problems mixing a half qt. of this Mobil DC+ HM 10w-30 in a 5,000 mile 4-banger that calls for 5w-20?