I was under the impression that none of the oils thinner then 5-40 were rated for use in our older diesels. I see no reason to run anything but the 15-50 Mobil 1 "red cap" even my 6 cylinder cranks fine when cold soaked, and oil pressure comes up quickly. (Then again I don't live in New England.....)

Just some random thoughts. I believe Dave M. remarked that Mobil 1 was good for 4% soot, even with each engine developing different levels of soot based on internal clearances, state of tune, driving styles city/hwy, etc, of all the oil analysis that people have shared on this forum, I have not seen any yet where soot has come close to approaching this 4%, and many of these where done at 10k miles. I would think the cheapest alternative would be to run to 5k miles the first time with Mobil 1, and use a topsider or mighty vac to pull a sample, if the analysis comes back good, no need to change it until 7500-10,000 depending on what the analysis shows.


The arguement that I thought made the most sense, was to use synthetic in the 60x series motors, with their hydraulic lifters. For the 617 engines, use it if if you feel better about doing so, or if cold starts are an issue, otherwise save your money and stick with a quality dino oil, such as Delo 400, etc.