On the Duramax forum I used to belong to the general consensus was that oil is oil up to a point. If you ran dino or some super-expensive top-notch bougie oil and tested them both for wear at 5K you'd probably not see much of a difference. However, if you ran it past 10K and sent a sample in for testing you'd see a difference in wear and service life. The synthetic is great for extended drain intervals but early on in the oil's life it won't make much of a difference performance-wise. If you ran a bypass filter system there were members running Amsoil upwards of 25K between oil changes.
I ran Mobil Delvac 1300 Dino 15W-40 in my Duramax all the way up to 180K when I sold it with zero issues. 10K OCIs with samples sent to Blackstone Labs.
Now as far as the CTD goes...I run the Valvoline Premium Blue 10W-30 and get it straight from Cummins just as @NIsaacs suggested. Best price I've found. Stocked up with oil and filters for my next 3 oil changes. Same with fuel filters from either Geno's or even Autozone had them in stock for a similar price. OEM and or Fleetguard. Not going to skimp on cheap fuel filters on my $80K truck.
I ran Mobil Delvac 1300 Dino 15W-40 in my Duramax all the way up to 180K when I sold it with zero issues. 10K OCIs with samples sent to Blackstone Labs.
Now as far as the CTD goes...I run the Valvoline Premium Blue 10W-30 and get it straight from Cummins just as @NIsaacs suggested. Best price I've found. Stocked up with oil and filters for my next 3 oil changes. Same with fuel filters from either Geno's or even Autozone had them in stock for a similar price. OEM and or Fleetguard. Not going to skimp on cheap fuel filters on my $80K truck.
