I tell ya Last summer I mixed a 50/50 brew of Pennzoil 5/20 and Pennzoil HD 15/40 and run it from May/03 till Nov/03 . The oil pressure was only a small bit higher when cold opposed to a 10/30 dino used previously and gas mileage was not affected compared to the straight 15/40 . Both these oils use the Shell VII so compatibility is not an issue . Through summer when cold oil performance is not such an issue this is a good way to get 5 buck a quart lasting ability for a buck fifty in engines that can run this weight . I think probably the Delvac 1300S and the Mobil Drive Clean + would make a good brew for summer use also but a guy would not get quite the hefty additive pack that the Pennzoil offers . I know there is some mixers out there so join in with your brews !