A cooling system for an engine includes a radiator and a reservoir. The reservoir includes upper and lower chambers and a conduit providing fluid communication between the upper and lower chambers. The upper chamber is usually in fluid communication with the radiator and the lower chamber has an opening that can open to the atmosphere, wherein the lower chamber is positioned below the upper chamber. The conduit having first and second openings, wherein the first and second openings are positioned respectively in the upper and lower chambers.