I need cooling system help

[avdcav]

Relax on the oil cooled thingy " it's just in jest
we can fun and crack some jokes on the forum too "

[Jaydee]

I think that cap with the pressure relief lever is not sealed properly. When your cooling system gets hot, natural expansion will lift the spring loaded cap seal and force fluid into the overflow, then when it cools it sucks it back in, lifting the tiny valve in the cap. Under the cap lid, there is another seal, to prevent air being sucked in. With your lever style cap, that is not sealed.
Have you also removed the allen plug on top of the thermostat housing and bled out all the air?. That seems to be the highest point.
JD