Anybody still using 30 weight CJ-4 oil in a Navistar 7.3L IDI

30wt?
What wrong with 15w40?

single weight oil is old technology, that’s why you can’t find it.

 

Yea you can. Shell makes Rotella T in straight 30 weight. You can get it at Wal Mart. It might be "old technology" but so is the IDI 7.3.

 

CK-4 is better than CJ-4, it is just an improvement and acceptable to use.

 

API CK-4 oils exceed the performance criteria of API CJ-4, CI-4 with CI-4 PLUS, CI-4, and CH-4 and can effectively lubricate engines calling for those API Service Categories. When using CK-4 oil with higher than 15 ppm sulfur fuel, consult the engine manufacturer for service interval recommendations.
Oil Categories

 

CK-4/SN oils, not CK-4 oil.

 

I too was the last holdouts on straight wt. oil. Synthetic too, just not what I was used to. Slowly, due to the cold weather, I began with 10-30 for cars, and always 15-40 for my trucks, but wanted straight weight for classic cars, small engines, and such. I always thought synthetic was this miracle fluid from the space program, and reluctant to use it, but have come to realize, it's basically regular oil with synthetic additives. In a diesel today, I'd run what the manufacturer recommends. To be honest, I think it's all a big ripoff and all oil comes from a tank the size of a stadium in Houston. I use Walmart oil in my Jeep. I read, Walmart oil is the #1 selling oil in the country, and is really repackaged Quaker State. Nice, huh? I'd go with Rotella 15-40. It worked the best for me.