I do alot of short trip driving so I get a little fuel mixed in with it and it's even thinner. On the last change I used Mobil Drive Clean Plus HM 10/30 w/ 1 quart of 10/30 M1. I wanted something a little thicker for the 95+ degree summer. Looks like I got it because I get at least 2MPG less than I got with Mobil 1.
I know this is just theory, but what would I end up with if I mixed 3.5 quarts of M1 10/30 with 1 quart of 15/50? Would it still be a 30 weight? I know the only answer is probably a UOA, but I thought maybe someone else had already tried this and could chime in.
Thanks