1987 Ford 302, new thermostat, water pump, radiator, and clutch fan. Heater core is bypassed temporarily to eliminate it from the equation. It won’t build pressure in the cooling system so I rented a coolant pressure checker. I pumped it up to 16psi with the motor cold and it held and didn’t leak anywhere. So, I started it with pressure still on it and it crept up until I bled down to 13psi where it held. So, I shut it off, bled the pressure off and restarted it hot. Letting it idle and reving it up it never builds pressure. I put cardboard under it and nothing is dripping. It only has an idiot light for temperature so I don’t know how hot it actually is. I’m scratching my head as I’d expect it to be leaking somewhere. Compression tested it and all cylinders are 170-180psi.