I was wondering since in the summer your oil heats up and thins out. So having 10W 30 oil in the summer since its a thicker viscosity oil will help coat your engine but using 5W 30 in the winter helps. Or am I wrong on this.

 

All oil is that xW-30 has the same viscosity at operating temp. oil never "thins out" but at cold-start up temp a 0w oil will have a viscosity closer to operating temp providing better lubrication on start up. whereas a 10w oil will be farther from operating temp viscosity and provide "worse" start up lubrication. if you can you should run 0w!

 

x2. The second number (30) is the operating temp viscosity. The first one being the cold start viscosity. Some run 5w30 in winter for better cold starting lubrication. If you wanted a thicker oil for summer, like if you have low oil pressure at hot idle, you should run an Xw40 wieght, like a 5w40 or 10w40.