Oil viscosity questions

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Apr 12, 2024 | 06:27 AM

#16

slowmans

Cargo Master

Joined: Jan 2006

Posts: 3,013

Likes: 90

From: SE. MA

I live in New England and we see a broad range of temps, I only put on between 6k-7k miles a year and half of those are usually towing. I have used nothing but 5w-40 since 2006 in all of my diesels and have had great results. I think if you are towing you should use a 5w-40 and after seeing many posts of potential damage from running a 15-40 I would personaly stay away from it......Just my $.02

Apr 12, 2024 | 08:28 AM

#17

rufushusky

Cargo Master

Joined: Jul 2011

Posts: 2,679

Likes: 983

From: Walpole, MA

Quote:

Originally Posted by Boaterguy

Because 5W-40 and 15W-40 are the same viscosity at operating temp. The 5W-40 will flow better in cold weather and cold starts.

Obviously, a 5W will flow better than a 15w oil. Low temp cranking and pumpability is tested at -30*C and -35*C, respectively for a 5w and at -20*C and -25*C for a 15w. At operating temp, they behave pretty much the same one minor difference is 0w, 5w & 10w-40 oils are allowed a lower high temp high shear threshold of 3.5 cP compared to 15w, 20w, 25w and monograde 40 weights that are a 3.7 cP. However the min and max kinematic viscosity thresholds remain the same. That said the 6.7 isn't a shear monster like the 6.0 HEUI based PSD's, so not a big deal on these applications. Further a 40 top weight oil shearing down to a 30 top weight oil without accompanying accelerated wear rates is really nothing to get excited about.

IIRC the 2011 and into 2012 engines had really tight bottom end clearances so it didn't appreciate the less pumpable 15w40, IIRC it was in 2013 or 2014 FoMoCo introduced a but more slop in the bottom end to be more tolerate of 15w40. That said I am in the minority of folks on this forum running a conventional 15w40 for the summer/towing season.

On the UOA front, just cause I have them in front of me from work, Cat's SOS lab does report on fuel and soot, however soot is as a percentage of acceptable