Ford Industrial 172

[Loaderman22]

Silly question & I think someone on here would know the answer right away. I have a Ford Industrial engine 172 gas and I put a new radiator cap on it, but I think the temp/pressure is too high because there isn't any fluid in the overflow, despite the radiator being rather full of coolant and me running the engine for an hour plus. I can hear bubbles so I'm thinking it's getting hot enough to bypass the cap, but overflow is dry. I'm wondering what cap I should be using?

 

[John0829]

Ford 172 uses a 4 psi cap and the radiator should have JUST enough coolant to cover the top of the core.