Originally Posted By: k1rod
Part of the reason I think 5W30 might be OK is that I have read a few posts indicating that 5W30 is what is spec'd for this same car in Australia and Canada. That would seem to indicate that the 5W20 was a US/CAFE mandate type decision rather than a technical based one. Also, several posts have indicated that 5W20 is a better oil but doesn't 5W30 have a stronger film strength? I live in Phoenix where the temperatures can hit 120 deg in the Summer and seldom get down below about 30 deg in the winter.
If you don't mind the potential warranty hassle (which is incredibly unlikely anyway), you can certainly use the 5W30 and there will be no real adverse effect. Yeah, I actually think the lighter weight would be 'better', but the difference is minimal, more so in your climate--and as you said most 5W30's shear down close to 20W after a short period anyway.
But don't get hung up an all of the logical fallacies which surround thicker oil. "what they use in XX country" doesn't really matter. You don't live there, so why is that an issue? Why do THEY choose the oils they do? It isn't all about CAFE (availability and their regulations play a part as well). Also, thicker oils don't necessarily have higher film strength when the oil is under extreme pressure (in some cases, the inverse is true, thinner oils actually create thicker films). And film strength is just one parameter important to oil and wear. There are many other considerations as well (cooling and lubricating engine oil seals among them).
If I were in your shoes, and assuming I didn't have another vehicle which used 5W30, I'd probably use it up, then buy 5W20 when it's gone.