i was looking at the parts house the other day and i was wondering if just reguler old 40 weight would go fine in this 7.3, i'm currently running delo 400 15w40 but its the new low emmission stuff. i didn't notice delo 40 weight having the cj 7 rating. so whats the differnece between the 2? would it hurt to run it?

 

I wouldn't do it. You'd lose all the benefits of it being 15 weight oil at start-up. In other words, when cold, it will be REALLY thick. Very tough for the LPOP & HPOP to move easily.

On a side note, I didn't really care for how Delo ran in my truck. Romped a little when cold, and noisy. My truck REALLY likes 5W-40 Syn Rotella.

 

the 40W will be slow cranking and hard starts when cold. I switched from Rotella to full synthetic Rotella and major improvement. I would not run straight 40w in my 7.3 unless I lived where temps never went below 80 F.

 

I just bought some Rotella Synthetic (5w40) last night at Autozone reg price 19.99 sale price 17.99. Not sure how long the sale is for, but I will try another store today and buy some more.
Jrod

 

Look on the container of the 40w and it has to say cg-4 (or higher) along with SL (or higher) to be used in our engines.. see your owner manual.. copied from the owner's guide supplement -- "Do not use oils labeled with only one of the following category designations, SG, SH, CE CF-4 OR CG-4, as they could cause engine damage."