Spring is coming up, and I'm planning on changing the oil in my 1986 Porsche 944 Turbo from its winter 15W 40 weight to its summer 20W 50 weight. However, tody I saw the 2009 Porsche recommended oil list where Porsche now recommends synthetic 0w 40 for all it's cars, dating back to 1984. 0W 40 sure seems awful light for my engine, especially since it was designed for a heavy-weight oil. Car has 83,000 miles and does not leak. What do you guys recommend?