I have a 2000 turbo with a little bit of a rattle. I would like to put some heavy oil in it. What is the heaviest oil I can put in this car? It has 150,000 miles on it.

I did a quick search and did not find any on this regard (please keep in mind that i am at work :D) We bought a 2007 vw beetle and had some questions about the oil... What type of oil does it take? My wife went for an oil change and they said it takes synthetic (car did not come with manual...