I use Rotella T. It's about $10 a gallon. A lot of guys hear use the synthetic stuff. I know that Amsoil is really popular, and I'm sure it's great. However with the dpf and egr dumping fuel that does in fact get into the crankcase, I don't think the longer miles between oil changes that synthetics promote is a wise decision for your engine. 5000 mile changes seem to be a better coarse of action, and synthetic is too expensive for that rate of change. Just my opinion for this particular engine/emission configuration. If you remove your dpf and thereby stop the regen cycles, this problem of fuel in your oil goes away.
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