What oil certifications are required for the 7.3L? I see CJ-4 thrown around a lot, is that the big one? Just trying to learn more about oils.

Also some oils say "for use in 2007 and newer diesel engines." where some others say "for use in pre-2007 engines and 2007 or newer engines off highway."

I have to assume this has something to do with ULSD and LSD but, what exactly?

 

CJ-4 is an American Petroleum Institute spec for diesel oil. You'll see CJ-4+ and CI-4 now also which is backwards compatible with a CJ-4 engine.

The 2007 and later oils are designed for diesels with particulate filters. They have less stuff like sulfur, phosphate, and sulfate ash in them which results in lower exhaust emissions and less particulate filter clogging.

A handy trick for the API spec is: if it begins with C (CJ-4) it's for a Compression ignition engine. If it begins with S it's for an engine that uses Spark plugs.

If you want to learn more about oils check out the bobistheoilguy forum.