Synthetic 15w-40 vs 5w-40

[SOHCman]

Exactly.
Not sure why CAFE was brought up in this thread. Neither grade is resource conserving.

CAFE was brought up earlier to make a point about thick vs thin protection. I believe it was due to the CAFE standards making OEMs look toward thinner as a solution to meet standards. This is of course possibly at the expense of protection depending on the engine we are talking about and how much the design shears oil.

 

[ruSSrt]

It's 5.9 cummins! Put some 15W-40 and forget it. I've used Delvac Super 1300 15W-40 for over 100k with changes every 5k. I maybe get two oil changes a year and I never had any oil related issues. Purrs the same as the day I got it.

 

[4WD]

It's 5.9 cummins! Put some 15W-40 and forget it. I've used Delvac Super 1300 15W-40 for over 100k with changes every 5k. I maybe get two oil changes a year and I never had any oil related issues. Purrs the same as the day I got it.

FF in DMax ….?