Just a data point. Doesn’t answer the ~should~ part of your question….
With 15w40 at operating temp, the well-worn 1962 engine in my 1951 truck registers 15 psi at idle and pegs the 30 psi gauge with any sort of throttle input. On a really warm day, if I have the idle turned down to 500ish rpm, pressure might creep closer to 10 psi.
I’ve been told by knowledgeable folks that it’s more than adequate.
