m/c is shorthand for "motorcycle". Basically, I was always using oils specifically formulated for motorcycles, so that was a constant, and all were the same 10W-40 grade. I obviously didn't keep using Mobil 1 m/c oil.Looks like I need to do some trial and error to see which oil suits my engines needs best. Motul has a 5w30 with SP rating. When the Stinger was brand new I used M1 and then M1EP. I noticed a lot of soot around the exhaust tips. All the soot kinda turned me off of M1 products. I switched to Total Quartz because that is what Kia recommends and the levels of soot was definitely reduced. Thanks for the advice. Stupid question, what are m/c oils?