Forgot this, does your overflow tank have a pickup tube in side. Also I don’t see a vent hole in the tank. Under pressure antifreeze won’t go into the tank coz there isn’t air escaping the tank. If would happen to get in the tank there has to be a tube to suck it back into the rad. I drilled and installed 2 90* 1/8x barbed fittings with a clear hose to see the level of antifreeze in the tank.