Engine cooling system vent means

In an engine cooling system, a thermostat housing having first and second chambers, a coolant inlet in said second chamber, a coolant outlet in said first chamber, a first aperture intermediate said chambers, a thermostat means in said housing intermediate said chambers for controlling coolant flow from said inlet to said outlet through said first aperture, a second aperture in said housing intermediate said chambers, the improvement which comprises fluid flow responsive vent valve means in said housing for closing off said second aperture when the coolant level rises in said housing as when coolant is flowing in said system while allowing air to escape through said second aperture as during filling of the coolant system, wherein said vent valve means comprises a valve housing defining a chamber therein, a valve inlet and a valve outlet in said valve housing, a valve seat adjacent said valve outlet, and a means for closing said valve outlet, said means for closing said outlet comprising a spherical ball float adapted to float in the coolant and seal against said valve seat, said valve housing further comprising a generally cylindrical adapter having a bore therethrough of smaller diameter than the diameter of said spherical ball float, and groove means on one end of said adapter for permitting air to escape from said first chamber through said bore and said groove means to said second chamber.