I’m a new member with my first post and a couple questions about oil. First off, I’m not a mechanic although I’ve worked on cars since I was 12 and I’m not an engineer, although some friends say I should have been. I just ordered a 2021 longhorn anniversary with eco diesel hoping they have fixed the previous problems. Question 1. Engine oil was changed from 5-30 to 5-40. Don’t understand why they would think 30 weight is heavy enough for a diesel. But they left the 5 weight cold weight alone. Most diesels I’ve had used 15-40. Ask any mechanic or engineer when the most wear on an engine occurs and the answer is the first few seconds of cold startup. Cold start doesn’t only mean freezing temps. It means any ambient temp that the engine has cooled down to over several hours and most of the residual oil on the bearings etc has drained off. Remember, a diesel has very high compression ratio. This one is 16-1. Most gasoline cars are 8-10-1. Diesels have a lot more stress on bearings etc every time a cylinder fires and drives the piston down. A 5 cold weight oil gives very little protection compared to a 15 weight. For the possible gain of a fraction of a mile per gallon fuel saving. I’d like to see at least 10-40. Question 2. Why is the eco diesel oil spec 12991 an API SN? S is for spark which means gasoline engine. Instead of a C spec which stands for compression (diesel) such as CH4 etc. Diesel oil spec is in there for a reason with required additives for soot and several other things. Im concerned Fiat Chrysler is concentrating so hard on fuel mileage, they are ignoring engine wear and therefore engine life expectancy.