Tell your brother to turn the night light off. Dual rated api sn ck4 15w-40 should be good enough in a smoker. Don't know anyone who would use that thin expensive oil in a burner. So forget all of that. Could also try 10w-40 or go 20w-50.
And before any woman starts mouthing about it being too thick I've ran 20w-50 in place of 5w-20 in my bygone ford out of curiosity over noise reduction and ran it like that for a 6k interval before going back to 5w-30 since it wasn't much noise reduction but a slight mpg hit in the first 10 minutes of warm up. Literally wont hurt an engine to go slightly up when its burning. If anything it hurts the engine less since there will be less carbon on the pistons and catalytic converter.
But as with anything why is it burning? have you tried the basics like the pcv and a strong engine flush.
What year, mileage, intervals, oil type, ect.