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Discussion Starter #1
What would happen if I occasionally ran 10W40 semi-synthetic oil (like the kind you run in gas engines) in my 7.3? I can get the 5qt jug of Valvoline semi-synthetic for $13 whereas regular Rotella T or other diesel oils are $11 for 4 quarts. Has anyone tried this or is it strictly not recommended? I was thinking about using the 10W40 semi-syn every other oil change.

Also, the truck is mostly a daily driver and occasionally tow a 6,000# travel trailer locally.
 

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Don't run non-diesel rated motor oil. If it is rated for diesels you can run it in both gas and diesel engines.
 

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Discussion Starter #3
Just did some Internet research. Found out any oil with GF-4 rating must have less than 800ppm of zinc which is critical for diesels. Shell Rotella-T contains 1.2% or 1200 ppm from what I've found. While there's probably other reasons not to run it (detergents, etc) the low zinc content rules it out.

I'm thinking of trying Schaffers 7000 (semi-syn) or 9000 (full-syn) now. It's not cheap, but seems to have earned very good reviews.
 

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You also need the anti foaming additives for the high pressure oil system:thumb:
 
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