Well here goes my first post, hoping someone may be able to enlighten me a bit Getting ready to do an oil change for my 02 Camaro z28. Used to use the 0w30 GC, but I don't have any more left. I was considering putting in either 5w30 or 10w30 Penzoil Platinum or Ultra Platinum, and was wondering what others thoughts were on the use of one oil over the other. More specifically looking at the specs on Penzoil's website for the above mentioned oils, the NOACK volatility of the 5w30 oils are roughly twice as high as the 10w30 oils. Owners manual on car calls for 5w30 preferred, or 10w30 is acceptable in temperatures above 0 F/-18 C. Car is driven solely in socal, so we definitely don't ever get temps below 0 F. I actually just checked and the record low temp over the last 25 years was 30 F for the city I'm located in. As 5w30 is the recommended oil according to the owners manual I was just going to put that in, but when comparing the specs on Penzoil Ultra Platinum 5w30 and Penzoil Ultra Platinum 10w30 I noticed the NOACK volatility of the 5w30 is 11.5% vs only 5.7% in the 10w30, and the Platinum(non ultra) shows a very similar trend with 10.1% NOACK volatility in the 5w30 and only 4.7% in the 10w30. Given that I never get temperatures below 0 F, would the 10w30 be better in my case due to the huge difference in NOACK volatility (or some other reason)? I'm a total noob as far as oil stuff goes, so I would really appreciate any input from someone more knowledgeable on this topic. Also if any one wants to chime in on which oil they would pick, please state the reason for choosing one over the other. Thanks so much.