Duramax and a HEUI diesel are night and day different...

Just avoid running extended oil changes on a HUEI truck...

I use Rotella, DELO, & del vac they are all good

i know that, was just saying to the quality of scheaffers oil.

I would just get whatever is on sale, UOAs one brand vs. another are so close, just pick based on price.



Dmaxs are maybe the easiest engines on oil, if you do UOAs you can run oil longer on a PSD you just really need to watch oil viscosity cause it can drop very quickly. IMHO not really worth it.

Rottela T for regular oil and Amsoil with a bypass system for synthetic, cost more up front but intervals are alot longer, I run mine for 25k and test good but I change it anyway, I have a 6.0 and been doing this for last 200k and I have 250k on it with no issues, at times I would put 5k on in 3 or 4 weeks. just put 2k on in 2 days,talk about tired:s:

The kind that gets changed! :tu:

Forgive me if this sounds intellectually challenged, but its from a hard headed friend. Is there any reason NOT to run synthetic oil in a 1999 7.3L?

Cost?

Other than cost...IMHO no. I know some people claim that you will start leaking or you can't mix conventional and synthetic or once you go synthetic you can't go back to conventional...etc.

I have never ran into any of the issues that people claim with synthetic oil.

I would say on how long your oil last would be on your driving habits no?