sour cream problem

I would say it should be fine for cooking purposes, and most likely for using as a topping. While separation did occur, the flavor shouldn't be disagreeable (of course, you're in a better position to verify this than I am!). Try making a sour cream pound cake or using it in pancakes. Or, for a savory use, make a dip with it and caramelized red onions.

not sure what its for yet-bought as staple. it's curdled and separated into whey and tiny curds. i stirred it and it doesn't mix back into previous form. package doesn't give fat percentage.
any suggestions? it's 16 oz carton.

What are you going to use it in? Depends on how much fat is in the product.

Should be fine. Lots of fat, so it's rather forgiving.