On my Autocar the over flow on the top of the raditor there is a round maybe a inch high and a inch and half across its like a round cap that the 3/8 inch hose hooks to. Here lately as it idels on high idel it will push water out the fill cap and none will flow from the 3/8 inch hose. I tried to blow some air in the over flow hose but it won't let any pass though. My question is there a releaf spring that opens up or something where the round thing is on the raditor. The water temperature seems fine but should the water exspan that much to cause this ? Thanks Bill