I've generally accepted that 5W-20 is safe to use, and I used it for 65,000 miles on my '04 Honda CR-V. Now I have an '08 CR-V, and the K24Z1 engine has always been a bit noisy compared to the K24A1 in the '04. Curiosity finally got the better of me today, and even though I was at 40% oil life remaining, I changed it. I went from Syntec 5W-20 (5300 miles on it) to GTX 5W-30, since I plan to change it at the normal oil life interval, and I didn't reset the oil life monitor yet. I figure that's a few thousand miles until the normal oil change, so that's why I went with GTX at $4 a quart instead of $7 a quart for Syntec. Observations? It's noticeably less "clattery" than before. The fuel injectors do make a noticeable clicking, but there was always a clatter that was especially noticeable when cold. The engine was still hot when I changed it, but already it's quieter. At least I have an interval to see if stays quiet, especially when cold, and to see if there's any noticeable hit in the fuel economy. I keep a log of all the mileage and fuel purchases, so I should be able to see if there's any noticeable difference. If the gas mileage stays about the same, I might just stick with the 5W-30.