I just had my oil changed this afternoon and I have always used valvoline durablend. My new mechanic (moved to a different state) told me the only thing he would change about my service was the oil because Valvoline and Pennsoil have a lot of wax in them and can cause the motors to get "gunky." I have not heard this and my last mechanic said the oil and engine have been very clean. Is there really wax in these oils?