I just changed my oil for the 1st time other week and used Mobil 1 synthetic 10w-30 but read in owners manual that 5w-30 was actually supposed to be better..wanted to know if there was really any major difference and also what brand oil is the best to use?
It says 5w-30 because of C.A.F.E. Corporate Average Fuel Economy, has nothing to do with what is right. They wanted milage and enough protection to get past warranty with normal use.
That said some 5w-30s might be quite good, M1 5w-30 and 10w-30 whaen actually measured DO NOT perform well in this motor, the much thicker 0w-30 Castrol Suntec labled "made in Germany" performs great easily argued the best available oil for a stockish LT1.
If you are partial to M1 just try the 0w-40 or 5w-40 is you run across it.
Used oil analysis for Mobil 1 5w-30 and 10w-30 have historically shown them to be mediocre in this engine at best. Iron wear in particular is high. It is quality oil just those two are not well suited to this engine based on the measured results of wear metal in oil. Based on that same testing the Castrol Syntec does much better, part of that may be because it is thicker. -30 is a weight RANGE not a specific viscosity. M1 tends to be on the thin side of the range and the LT1 and even LS1 have shown a preference for thick 30wt and thin 40wt. oils There is a lot more going on than just viscosity but it is still a recognizable trend.
the 5w, 10w numbers are not comparable to the second number and do not affect the viscosity, most 0w-30 oils are actually thicker than either M1 5w-30 or 10w-30.
It seems certain regions are having it on sellthrough yet some other regions have fresh 07 date code CG. My store doesn't have it on sellthrough, but it hasn't restocked with fresh yet. I've had them pull inventories of other sister stores, and then had them bring it in