Which Oil - 15W-40 or 5W-40 - Cummins 6.7L

[Cody Evans]

Which oil is best for the 6.7L.

I've always run 15W-40 in all my 5.9Ls year-round.

I am looking over the 6.7L info; it says to run 5W-40.

My summertime temps get close to 100, and Wintertime temps can get down to 0.

Which oil is best?

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[SyN]

My personal opinion - In your region - A PAO synthetic 15W-40 would be a ideal choice. (But I always think outside the box).

Hundreds of UOA have shown/proven - that during hard use the 15W-40 viscosity has produced lower wear #s then 5W-40. (Not much lower - but lower)

Respectfully - any brand of HDEO 5W-40 will work perfectly fine - for your situation (If you don't tow med/heavy loads year round).

To your question though - There is No Best Oil!

You have to run the proper viscosity - according to your driving style/habits & Ambient Temps.

If you tow Med/Heavy 24/7 (Hot Shot) - I would run a 15W-40 (be it Conventional / Syn Blend / Synthetic). --> No Questions.

Otherwise - depending on your Climate / Region of living - Driving Style/Habits - a quality HDEO 5W-40 will work ideally - along with a well thought out OCI. (Don't Skimp on the Oil Filter).

All of this is just my Opinion!

Others will chime in with other advice.

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[6.7 Coal Train]

I run 5W-40 in a similar climate.

I don't think I'd run the 15w in 0-degree temps, and 5W-40 covers those warm temps as well.

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[dodgemark]

I run 5W-40 in winter, and in spring, I change over to 15-40 for the summer heat 2011 ram 2500 with 111,365 miles.

I have never had any oil or rattling noises problems.


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[AK Bob]

I run 5W-40 T6 all year round.


2014 RAM 3500 (Aisin) 3.73 4X4 Limited Crew Cab Long Bed DRW. Oil Bypass Filter, Fuel Filtration Kit, and 50 Gallon Aux Fuel Tank.

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[ECLIPSE22]

I run this Valvoline Oil (5W40) with a Fleetguard Stratapour filter.

So far, so good.

I have been happy with this product.

Temps I see are anywhere from 14 - 105 Fahrenheit.

Valvoline Premium Blue Extreme Full Synthetic Engine Oil 5W40 1 Gal - C774038GA (cummins.com)

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[watersupply189]

I run 15W40 full synthetic year round, and my temps get down to 0 or less at times.


2016 Ram Laramie 3500, G56, 6.7, CC, 4x4

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[Patriot MotorSports]

In the summer or median temps over 50-60 degrees F, I run 15w40 T6.

In the winter I run 5w40 T6 and not only do I see quicker warm-ups but a small bump in MPG averages on longer trips.

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