Engine cooling system and the reserve tank

The utility model discloses an auxiliary water tank. The auxiliary water tank (3) comprises a tank body (30), wherein a chamber is spaced on the tank body (30); a water outlet (32) and exhaust ports (33) are formed on the tank body (30); the water outlet (32) and the exhaust ports (33) are respectively communicated with the chamber; and the exhaust ports (33) are formed at the top of the tank body (30). Moreover, the utility model further discloses an engine cooling system using the auxiliary water tank. With the help of the scheme, the auxiliary water tank provided by the utility model can ensure smooth gas-liquid separation and can prevent liquid from easily accumulating in a pipeline in the engine cooling system.