Originally Posted by Bladecutter

The 229.5 spec allows for extremely long oil change intervals (15k+) when used in conjunction with a fleece oil filter, and provides better fuel economy than 229.3 oils.

229.3 oils are good for up to 12k miles, or one year, and offer better engine protection for extreme engine demand situations (racing, towing, etc). That's why 5W-50 is only allowed in the 229.3 spec.