Originally Posted By: Pablo
It's just not possible to answer this question without knowing the composition of each one of the oils. It wrongly presumes that all SAE 30's are the same or that all 10W-30's have the same base oils (for examples). So as written it cannot be seriously answered.
Oh, sorry about that. I use Formula Shell 5w-30. On the 30 minute highway drive home from work I use the a/c which robs some power from the old 4 cyl single cam engine. It's 100f when I start the car. I should get the best fuel economy if I'm using the grade that warmed up/or thinned to 10cst first. Using Formula Shell, is that grade the sae30, 5w-30 or 10w-30?
Thank you all for your interest!