Just traded in my 2003 and bought a 2021 and was wondering why they recommend 10w30 for summer and 5w40 in winter for the 6.7 diesel the choice seams odd. What do you all recommend.

 

My thoughts exactly…most just run 5/40 year round.

 

My 2011 calls for 15w40 above Zero temps and 5W40 at Zero or below or 5w40 Year Round. I keep it simple, I run 5w40 Rotella T6 Year Round. No issues at all, my truck likes the T6. I'm guessing the newer Rams like you folks have, now have tighter engine tolerances and to help boost fuel economy, is why the 10W30 is required rather than the 15W40. I have read where Mopar/Cummins mentions using Shell Rotella in the Owners Manual.

I would be careful and follow what the Owners Manual Requires since your trucks are under factory warranty.