Mystik JT-8 15w40, 2015 RAM EcoDiesel, 4,995 mi

[DoubleWasp]

OTR diesels have very low specific output compared to a light duty diesel engine.

In defense of 30 weight oil, there are very knowledgeable members here who have run 30 in their diesels without issue. Spectacular UOAs as well.

Not every engine is the same, though. I have not and will not run a 30 in an engine spec'd for a 40 any time soon.

 

[CT8]

Originally Posted by dnewton3
Perfect example of why paying for more does not always get you more.
The UOAs show the engine is in fine condition. Low wear metals and no contamination.
Honestly, it's probable that this engine in no way "needs" a 5w-40 syn, especially for 5k mile OCIs.
While under warranty, best just to do what you're told though.

The 5W buys you better below 0*F starting. The 7.3 Powerstroke engine cut off for 15W-40 was 17*f in the manual.

 

[bullwinkle]

I would be interested in seeing what a good 10W30 HDEO would do in an EcoDiesel compared to a 15W40, but as long as winter starts are good, there's not really any reason to not use 15W40.

 

[DoubleWasp]

Would be interesting to see, but in my experience, when an engine manufacturer runs away from a certain spec, there's usually a REALLY good reason why.

 

[Fraser434]

Originally Posted by BoiseRob


If this is a true statement, why are ALL OTR semi's delivered with 10w30 in the sump. They are THE "true" working diesels...



Reason being.... MPG. Marketing.

The OTR Class 8 manufactures put in millions of dollars into engineering to get +1 mpg. Thinner oil, less viscosity, less drag.

Every advantage they can find, they will exploit, now you see CK4 5W-30 and 10W-30 being OEM for the 12-14L engines. (with fine print, you can use 15W40). kinda like when ford switched to 5W-20.