CJ-4 engine oil……….

Wanted for my new(to me) 1991 7.3L Navistar diesel engine.
Yes, this is in a Ford F350. Of the service bulletin’s I’ve read, Ford is still recommending CJ-4, not CK-4 engine oils. Preferably a straight 30 weight.
Can’t locate 30 weight CJ-4 engine oil(so far).

 

Stumbled upon some Mobil Delvac 1Extreme 15w40 at the Walmart in Gatesville Tx. $22.90 a gallon. Bought 3.
They also had Royal Purple 15w40 at $29.90 a gallon, passed on that for now. I will see how this Delvac Extreme performs, as I don’t know if this engine ever had synthetic engine oil before, I am going to change out oil filter after about 500 miles or so. Maybe once more before changing at the 5,000 mi recommend interval.