Don't forget, that automakers, including Honda, do not ONLY have the end users' interest at heart when they specify or design things. Sometimes their hand get forced by the "expert Government auto engineers" in Congress. Even Honda succumbed to installing motorized seatbelts in the 90 and/or 91 Accord (remember those?). Not a choice any Honda engineer would of made on their own initiative
The government has draconian disincentives for automakers when they miss their fleet fuel averages. Every tenth of a mpg is pursued, and 5-20 is a direct result of that. It has been stated in a number of places (Ford doing so openly) that the main objective of 5-20 is better fuel mileage, not better motor protection. Motor protection is still OK, by all means, but not at all necessarily best.
Royal Purple sells full synthetic 5-20. I have posted about this before. The engineers at Royal Purple explained to me what is important is film strength not viscocity in and by itself. Sewing machine oil will protect better than 20w50 if the film strength is higher.
Now for RP I have been told, that the film strength of 5-20 is equal to that of RP 5-30, so it is the actual preferred lubricant because of the lower pumping losses. For most motor oils, especially of the dino variety, the 5-20 will have a lower film strength than the 5-30, because for dino oil, viscosity is one thing that enhances film strength at the expense of pumping losses (and fuel economy).
So without specific data to the contrary, I'd venture to argue that 5-30 is better for the engine, even the 2002, than 5-20. Especially in summer, Texas, Arizona, fill in any condition that dramatically raises underhood temperatures.
Winter in Minnesota? 5-20 will be easier on your engine than 5-30. There probably is no one-size-fits-all answer to the 5-20 or 5-30 question.
There is a good chance that synthetic 5-30 pours better in cool/cold weather than dino 5-20. Quick circulation on cold starts (where the majority of engine wear occurs) and stickyness of the molecular film to metal parts after circulation stops will do more to protect your engine than the viscosity of whatever circulates once the engine is running. This is my motivation for using RP. RP has molecular lubricity enhancers which is why I will do one dino oil change at 3500 before switching over to it for the life of the car at 7000.
As a final point of comfort for whatever you feel comfortable using: Have your oil analyzed by an outfit like Blackstone labs. Especially if you do this throuh the life of your engine you will see if disproportionate wear starts to occur from the increase of trace elements measured in your drained oil. This will also tell you if you are extending the change interval to long even if you are within Honda's service intervals.
John
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