Ok so I've been working around this cold temp starting stuff. Heres what I found out. We were badgering the man at the local diesel shop. Local being 3hours away in another state. The cummins manual says 10degrees F for 15-40. I use rotella. Rotella says -15degrees F. My dad called cummins (1-800-343-7357) and the man there said -15degrees F for 15-40 rotella. I called today and the guy had no idea he just kept saying "we only go by whats in the manaul" Also the guy at the shop said -15degrees for 15-40 He and rotella both said if you get a synthetic 5-40 your good down to -40 degrees and up to whatever the regular is good for, but its more expensive and harder to find? So what it boils down to is if your useing rotella. 1 cummins guy, 1 shop, and rotella them self says its good to -15. 1 cummins guy has no idea. Lets all call cummins and bother them about it till we get a real answer Anyway. I just thought I'd pass this info along and see if anyone else has heard anything about it.
Chris

 

Just switch to AMSOIL 15-40W, plug in the block heater and don't worry about it!

" AMSOIL Synthetic Heavy-Duty Diesel and Marine Motor Oil remains fluid at temperatures as low as -47°F (-44°C). "

OR the 5w-30

" AMSOIL Series 3000 Synthetic 5W-30 Heavy Duty Diesel Oil remains fluid at temperatures as low as -60° F (-51° C)"

And, extend your oil drain intervals and save the environment and your pocketbook!

And, if you're really worried install an Oil Pan Heater..

http://www.jcwhitney.com/webapp/wcs/...0101&langId=-1

 

I cant plug in at work and when its in the single didgets at night I have to leave my truck there.

 

Well Chris, my manual says to use 10-30 for -15F temps and that's what I did in WY & MT for eight years. My dealer was the one who pointed it out to everyone accustomed to using 15-40 even in the winter.