I ran redline 10w30 in my LS1 last year, but never 5w30 like GM recommends. I heard that 10w30 was better due to being a little thicker oil, that it would hold up better under high temps. But I did run mobil 5w30, and noticed that my engine ran a little quieter, which everyone said was supposed to happen with 10w 30. What is the difference anyways when hot ? aren't 5w-30 and 10w30 the same then because they have the same viscosity ? I have no idea then why my engine would be quieter with 5w-30. I've also heard GM only recommends 5w-30 for fuel economy, but is that true ? Basically, what I'm asking is since my car is only driven in the summer, would there be ANY benefit of running 10w-30 over 5w-30 ?