SAE 30 or 10W-30 for older IH FARMALL

[IH3444]

https://autosolutionlab.com/why-does-flat-tappet-need-high-zinc-oil/

Does Rotella 15w40 have zinc?​

Yes, Rotella 15w40 Oil contains around 1200 ppm of zinc.

 

[dennyd]

Modern 10w30 oils do not have the zinc needed for old engines with flat tappets. Most cam companies recommend a 15w-40 diesel oil for the higher zinc content.

10-30 diesel oils have plenty of anti-wear additives, Rotella is one, Lucas also a good one & always on sale at Fleet farm.