Well, I did a search of the forum and didn't find an answer to my question, so here it is:
Which is better for warm-weather use, and why: Mobil1 0W30 or Mobil1 5W30?
I've tried both oils and I found the volatility of the 0w-30 to be too high for my engine. I have an Acura RSX which has 160hp 2.0L four. I'm running the 5w-30 now and my oil consumption is too low to measure after 2000 miles. The 0w-30 may be OK for really cold weather but I wouldn't recommend it for mild climates.
