Quote Originally Posted by sdjimbo View Post
Hey everyone, I am sure this question has popped up before; my apologies.

I have a 12 3500 SRW with 165k miles.

I am currently running 15W40 and am about to change my oil.

With February, I am considering trying 5W40 for a few months.

I live in northern Virginia, so it doesn't get below 10F very often.

I just wanted to get some advice from all of you.

I have seen on other platforms that you get better MPG and cooler temperatures and stuff.

I thought I would ask the Cummins professional here because I trust the information you all provide to our community more than anywhere else.


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OK, I will say the opposite, so don't hate everyone.

I run the 5W40, specifically Amsoil, in my two-gen RAMS only because it's Amsoil.

Their cold flow test and general tests are impressive, but for some reason, 5W40 is the only weight oil they list for my 2016 and 2018.

Like you, I remember wondering if it was OK to run that oil year-round.

I called them, and they said yes, it is absolutely.

I also run it with their bypass system 60k mile filter.

I am not trying to sell you anything.

I prefer their oils based on the results of independent tests I have seen over the years and on my vehicles.

Plenty of other great oils are out there, and if you want to stick with 15W40, stick with it.

I can't say I have seen mileage increase or anything, but my Blackstone lab tests looked awesome before testing this oil.

I will say that if you have a 5th Gen, I won't screw around with any other weight of oil than what they call for.