synthetic builds deposits, cold weather needs thinner oil due to its materical make up oil with slug under code conditions thinner is harder to slug up in cold weather, Hot weather needs THICK becuase of molecular breakdown at hig rpm and high heat.

If you run a 5w-30 in a highrevving high compression high hp car your gonna cook the oil. run a heavier oil, Thinner oil can also bypass rings like water

slow engine like diesals use SLUG lol high comprression low RPM heat breaks down the oil. 10w30 is a good is good for a beefed up car. Turbo needs a special oil that will withstand its heat. Synthetics are just that synthetic They are good for Aluminum blocks and the like. Natural oils have impurioties and junk. Synth is a better oil for performace engines. Its viscosity is 100 times better than natural. Sytnthetics are engineers for high performance. Breaking in an engine with sytnthetics you have to stay with synthetics. and vis versa. Depends on your application. and what your putting it in and the region you live in.