What was the oil pressure on a CAT D6 9U back in 1956

[flatheads & vacuum tu]

The oil pressure gauge in my CAT D6 9U dozer died (it was made in 1956). The original gauge did not specify psi, but just had an operating range. I have the original manuals, and they just state to keep oil pressure in the operating range. Any new gauge will be in psi, so do any of you know what psi the D6 should run at?

 

[AJ.]

To my knowledge, Cat never spiffed oil pressure for any of their engines, the only info I got is to keep it in the operating range.
AJ

 

[rustred]

put a Guage on it and find out what it has for psi . i prefer one that is in psi .