Oil Type for 6.7L Cummins T Diesel

[Ram3500Owner1971]

After logging into mopar.com, going to owners manuals, selecting - Diesel Supplement Manual.

The manual states that you can use synthetic oil, and it says that you should use 10w30 for ambient temperatures above 0 deg F, and says 5W-40 Synthetic for ambient temperatures below 0 deg F.

It also says that using conventional vs. synthetic does not change the change interval, and you should follow the interval schedule.

What's the deal here? API CK-4 is the designation that must be used, and that can be found in synthetic and conventional oils. Why does it state conventional 10w30 for above 0f ambient, and specifically state synthetic below 0f ambient?

 

[mtnrider]

Not sure they make a conventional API CK-4 oil in 5w-40, think it's only in synthetic that's probably why?
My 2016 manual says 15W-40 for normal use and that is all I have used. Unless you are in the arctic I would not worry about using the 5w-40. My truck was just fine living in Colorado with 15W-40.

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[tjfdesmo]

The 2019 CGI Cummins doesn't call for 15W40 at all. I assume this is because of the hydraulic roller lifters, instead of the old reliable flat tappets. I plan to run either Rotella T6 5W40 or Valvoline Premium Blue Extreme 5W40, both are full synthetic, and easy to find. If Schaeffer's 9000 was more readily available I'd definitely consider it.

 

[dmekkers]

Not sure they make a conventional API CK-4 oil in 5w-40, think it's only in synthetic that's probably why?
My 2016 manual says 15W-40 for normal use and that is all I have used. Unless you are in the arctic I would not worry about using the 5w-40. My truck was just fine living in Colorado with 15W-40.

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That's what I read in my 2016 manual as well. Going that route full synthetic.

 

[chri5k]

Been running Valvoline Premium Blue 15w40 dino oil for 200,000+ miles. I change oil and filter every 7,500 miles.