Cummins 5.9: 5W 40 vs 15W 40

[ThisBigRoadTrip]

I run my truck at full GVWR permanently as we have a full time camper on a Ram 3500 with Cummins 5.9.
Hot and humid conditions. Usually around 30ºC (86F) ambient temps. Lots of hills. We are in Central America and will be in hot South American countries during the next oil interval.

Whilst trawling around for some truck info to add to my collection I came across this article:

http://www.dieselhub.com/maintenance/5.9l-cummins-engine-oil.html

It seems like a nice summary. One thing that stood out was the recommendation for:

• > 0ºF - Use SAE 15W 40
• All Temperatures - Use SAE 5W 40 Full Synthetic

I was just going to run with Valvoline Blue 15W 40 synthetic as it seems available here. Would the 5W 40 be better all round? And if either would work should they both be synthetic?|

Thanks in advance for your help.

 

[JLTD]

In that heat, 15w-40 will treat you well, and the Blue is a very good oil.

 

[SteveG4]

Yes. In your heat, a 15W-40 would be optimum.

Though, the Valvoline mentioned is quite good.

 

[bullwinkle]

You'll have less oil burn off in your conditions with 15W40. I use M1 TDT & Delvac 1/ESP 5W40 in mine, but I have a somewhat weak CP3 high pressure pump that likes high cranking speed to start below around 10F unplugged.

 

[bbslider001]

If you get the Napa version of their diesel fleet oil 15w-40, it is made by Valvoline as well and is usually on sale or much cheaper.

 

[Bighorn2500]

I live in Michigan and run 5W40 year round as an all season oil. I've seen temp's as high as 100 degrees and as low as -19 degrees. Usually T6, VPBE, or Delvac 1 whichever I can acquire on sale or with rebates.

 

[A_Harman]

The Cummins 5.9 is not finicky about oil at all. In Central and South America, any good quality 15w40 will work fine.