Oil weight for 2005 Gen 2 w/125k in Hawaii?

Unless you happen to live near the top of Mauna Kea, I wouldn't think the temperature there would ever be low enough to see any difference between 5W-30 and 10W-30. At very low temperatures, multi-grade oils are expected to have the same low viscosity as a single grade oil of the lower weight (i.e. 5W or 10W) and not become any thinner than a single weight oil of the higher grade (i.e. 30) at high temperatures. I expect that over the range of pleasantly warm temperatures you normally see on your islands, either of these oils would behave similarly to a 20W single grade oil, so it wouldn't matter which one you chose.

 

it should be on the oil filler cap

 

Yes, and in Owner's Manual, 5W30.

 

Any decent 5w30 synthetic should be fine. If you had weeks or months at a time with temps over 100°F, then I might consider using 10w30 (even then I might check hot engine oil pressure with a mechanical gauge first). You want the "thinnest" oil on cold starts that can still provide adequate oil pressure under typical "worst case" conditions when fully hot.

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That's not the way I understand the difference between 5W30 and 10W30. At high temperatures, they should both behave like a 30 weight oil. Certainly at low temperatures, the 5W30 oil will be thinner than the 10W30 oil and would provide better protection because it is able to more evenly coat engine parts.

https://www.autozone.com/diy/motor-oil/viscosity-5w20-vs-5w30-vs-10w30

 

What's your oil consumption like ?
If it is not excessive......like less than a quart in 4-5K miles......then there is NO reason to be messing with your oil of choice.

If it IS using oil......like a quart in 1-2K miles, then switching to a "high mileage" oil might be a good idea.