ISX CM2350 Oil Usage and Fuel Economy - Suggestions?

[Nilao]

Isn't this in the model range of the faulty valve guide seals?

You could take the exhaust pipe off and do a snsp test as well to see how much smoke it puts out.

Also take the oil fill cap off with the engine running snd see how much blow by there is. Should just be a light puff. If it looks like a old steam loco then your rings are shot.