I will always use synthetics after I saw a couple tests done locally. First test was to put oil and water into a blender and see how long it takes to seperate oil from water, the Mobil 1 seperated while the normal oil never went back to it's original state. Then there was the pour test at -10F or something the Mobil 1 poured like new and the normal oil came out thick and didn't look like something I wanted in my engine.