Good Evening, my neighbor with a VW TDI has been having slow starting and starting noise since its been super cold in CO lately, often at 0 or below in the AM. He’s running 15w40 Rotella and wants to go to the 10w30 for below 0F protection. I suggested the 5w40, but he doesn’t want the extra expense. Not garaged and no block heater or oil pan heater, not interested in any of those adds either. Is the 10w30 sufficient protection at colder temps?