I wrote AMSOIL an email about what they recommend for the 3.5L this is what they said:
In response to your inquiry, we recommend the use of our AMSOIL Series 2000 0W30 Severe Service Motor oil (product code TSO). This premium motor oil protects better in high temperatures than do the higher viscosity conventional and synthetic oils. Series 2000 retains excellent fluidity in extremely low temperatures, so it flows quickly and reliably to allow easy starting and immediate lubrication protection. This product may be used year round and is not affected by high ambient temperatures. The service life on Series 2000 is 35,000 miles or one year, whichever comes first. A complete description of this product can be found in the "PRODUCT INFORMATION" section of our website.
35,000 miles hahaha OMFG
Jeff
former 2000 Proton owner
Lehigh Valley, PA