Cooling system pressure

I am not getting any pressure in my cooling system. The van warms up properly and the heat works. No overheating but no pressure building on the systrm. I just did the inline filter and black flake mod and I don't seem to be loosing any coolant. I'm confused. Any ideas?

Have you replaced the cap? The same black flakes that result in the high idle when cold also obstruct the reservoir outlet channels at the small black hoses. I would pull the reservoir and clean the outlets and see if that helps.