[prime81]

Castrol Syntec European Formula(known as German Castrol), 0w-40. If ya don't believe me just search around the interwebs for oil analysis results and information on the base oils used in that specific formula.

0 weight is designed to lessen initial starting wear and tear due to the tight spec these engines have. Now as to 20, 30, or 40... just depends on the duty of the truck and temperatures it will be operating in. It regularly gets 100+ during the summers here while pulling my boat so I chose 0w-30, and as it so happens the european formula castrol syntec is 0w-30 only around here.

 

[prime81]

Made in German Castrol is 0w30 full synthetic (European formula), I use it in Subaru as 30 weight is what it takes. The 0w40 Castrol full synthetic European formula is made in Belgium, used by the turbo Subaru crowd.
I still have plenty of the 0w20 but when it runs out and at 80-90,000 miles I will switch to 0w30 myself. And to stop buying 2 weights of oil.

You are correct sir, I was remembering incorrectly what I put in since it was nearly 5000 miles ago.