Patent ID: 6990931

Claim:
A heat storage tank for storing a coolant of a liquid-cooled engine, the heat storage tank comprising: a tank body in which the coolant is stored while being substantially thermal-insulated, the tank body having an inner wall surface for defining a cylindrical opening portion at one end side; a coolant passage portion having an insertion portion to be inserted into the cylindrical opening portion in an axial direction of the cylindrical opening portion, the coolant passage portion defining therein a flow passage communicating with the tank body, through which the coolant flows into and flows out of the tank body; and at least two O-rings for sealing a clearance between the insertion portion and the inner wall surface defining the cylindrical opening portion, the at least two O-rings being disposed between an outer wall surface of the insertion portion and the inner wall surface defining the cylindrical opening portion of the tank body to be lined in the axial direction of the cylindrical opening portion; wherein: the at least two O-rings comprise first and second O-rings provided to be separated from each other in the axial direction; the first O-ring is disposed to directly seal a clearance communicating with an inner space of the tank body; and the second O-ring is disposed to prevent air from being supplied to the first O-ring.