Is there any problem with running Chevron Supreme 10W-30 in the summer, and Pennzoil 5W-30 in the winter? Is there any reason to pick one brand of oil and stick with it? I like the Chevron for the price, but it is hard to find in 5W-30. Pennzoil is much more common. I am not sure I want to use a 10W-30 year round, as it can get cold in PA winters. What do you guys think?