Your Mobil 1 Choices:
Mobil 1 0w40 only meets the specs of a CF rated diesel oil. I would not trust it to handle the soot like a CI-4+ or CJ-4 rated oil.
Mobil 1 TDT 5w40 is a CI-4+ rated oil and would be your best choice YEAR ROUND.
Generally speaking, Just because an oil has a high amount of viscosity improvers like Mobil 1 0w40 does not make it a better oil. That only means it is having to overcome some weakness in the base stock viscosity. I would much prefer a Class 4 synthetic that has a great basestock and therefore does not need a high level of VI to make it perform. There are many areas of the oil spec like TBN, flash point, pour point, cSt at 100C, etc to determine overall performance.
Unless you are running your CRD in the Antarctic during the dead of winter, I cannot see why you would need any winter oil below a 5w40. Like I stated before, even the class 4 10w40 or 15w40 would flow at temps we have in all 48 states. If you are worried about winter flowing, get an oil pan heater pad and plug it in. Doing that you would even be able to use a 15w40 conventional oil at -50F comfortably (we did in Alaska).
If you are looking for just economy, I would think that the HDD 5w30 CI-4+ Amsoil would be the better choice.
Look... the Mobi 1 TDT is a pretty good oil. It gets down to a nit picky game at that point. The Amsoil's will perform great and even beat the Mobil 1's. But unless you are going for extreme oil change intervals I wouldn't worry. You would want to do oil analysis anyway. At that point, with the cost, just change the Mobil 1 at normal intervals and forget the picking over details. I ran a 1996 Cummins to 1.4 million miles using 30K oil changes with Kendall 15w40 conventional oil and had NO major problems. The truck is still running today with another company and still has not had an overhaul.
Check out
www.bobistheoilguy.com forums if you want to see the results others are having with various oils. You will get overloaded with details there. Just don't try to sharpshoot those guys there unless you a certified oil wizard.... They are some real knowledgable people, but they are very friendly to questions.
Have fun! Stick with the Mobil 1 TDT if your heart wants to.
Now you can start getting picking about oil filters! They are equally as important as what oil you are using. But that is another discussion that will start a stampede!
