I have a '98 SLK 230 that will need an oil change soon and I would like to change(?) to an AMSOIL full synthetic but my car manual said to contact the dealer for his recommended viscosity. I would appreciate your opinion on what I should use. .

I have been running 0w-30 in my Porsche designed Ford v6 and it loves it. This is recommended for cars that use 5w-30 or 10w-30. I read somewhere that 15w-40 was a MB recomendation and if so, I would op for a 10w-40 unless I hear otherwise..

Oh I live in central ca and see temps below 20F in the winter and above 120F in the summer. Thanks for any help with this one..:p