[Boog]

What is up with today's motor oil ratings?
For over a year I have found our Walmart isn't stocking a full line of oil like they used to. Right now they mostly have full synthetic in 0w20 or 5w20 "made from natural gas" on the shelf. And what's more, it is labelled for high mileage engines.
It has long been my understanding that the low first number is for cold weather startups and the second number is for full operating temp viscosity. And a heavier rated oil in the past was recommended for higher mileage engines.
Are they rated differently these days? Even on our modern engines 0 or 5w20 sounds too thin for good protection to me.
I'm changing oil in my 2003 Tahoe with 300,000 miles on it. Surely there is enough wear in it that a heavier oil would be of benefit to it. That truck sees over 100 miles of highway every day.