SAE 30 vs. synthetic 5w-40

[Bdub]

I have a 91 f-250 with the idi 7.3. the manual calls for SAE 30 motor oil but is it alright to use synthetic 5w-40 (Rotella)

 

[Drew99GT]

Rotella 5w-40 would work fine. If you do use SAE30, make sure it's a CJ-X heavy duty rated oil suitable for diesels, like Rotella SAE30.

Another great option would be Rotella 10w30 if you could find it.

 

[D-Roc]

I would have no qualms about using the Rotella T Synthetic 5w40...Not sure if Shell makes a CJ4 spec 30 weight.
But if you need 30 Rotella comes in CJ4 as Drew mentioned.

 

[ottomatic]

I had a 6.9 IDI. I used Pennzoil hd 30 its whole life with me. It was stolen with 450,00 mi onit. I would use the 30. Recently I tried 5w-40 in my 99 7.3 . It didn't like it

Go here: https://bobistheoilguy.com/forums/posts/866047/

 

[Jaymus]

And, what did it say it didn't like about it? Those Ford diesels last forever, anyways.

 

[ottomatic]

Originally Posted By: Jaymus
And, what did it say it didn't like about it? Those Ford diesels last forever, anyways.


It said "This synthetic stuff is giving me lower oil pressure, I'm starting to have oil seeping every where and my engine is running rough especialy at idle. So please Otto put me back on 15w40, after being on conventional 15w40 for 3000,000 mi this synthetic stuff is causing me health problems".

Which I promtly did