Yeah, the thicker oil sticks better to the cylinder walls which helps to seal the rings better (Lamen's terms). I've always run my Duratec on 10w-40 (I'm up North), and never any thinner, and I get better power and response too. Thicker oil also offers better protection. The reason thin oils have gotten so common these days, is because the EPA (Environmental Protection Agency) pushes thinner oil because it has less drag on moving parts (gives better fuel economy), and the oil pump doesn't take away as much HP to pump thinner oil. So cars with it use less gas over long term. Now this doesn't seem like a significant loss, and it isn't, in one car, but if everyone in the U.S. runs 5w-30, that adds up to a LOT of gas, and pollution over a year's period. But I'd rather go for the extra protection of thicker oil in my cars, and so far, it's paid off
