An expansion tank for a vehicle with dual cooling lines includes a first chamber with a first fluid pressure, wherein the expansion tank includes a first fluid connector in fluid connection with the first chamber for connection to a first cooling line, a second chamber with a second fluid pressure, wherein the expansion tank includes a second fluid connector in fluid connection with the second chamber for connection to a second cooling line, wherein the first chamber and the second chamber are in fluid connection via a pressure actuated two-way valve that acts as a one-way valve open in the direction towards the second chamber at differential pressures between the second fluid pressure and the first fluid pressure below a first predetermined differential pressure threshold and opens also in the direction towards the first chamber at differential pressures above the first predetermined differential pressure threshold.

A pressure adjustable radiator cap contains: a body screwed with a pressure adjustment assembly connected with a covering assembly. The pressure adjustment assembly includes a rotatable knob, an adjusting bolt, a push spring, and a holder. The covering assembly includes a rubber gasket, a lid, a positioning spring, and a coupling sleeve. The pressure adjustment assembly abuts against the push spring by using of a connection disc on a lower end of the adjusting bolt, and the riveting portion on the lower end of the adjusting bolt contacts with the coupling sleeve so that the pressure adjustment assembly is connected with the covering assembly. The rotatable knob is rotated to actuate the adjusting bolt to revolve so as to change a screwing force between the adjusting bolt and the body, thus adjust a closing pressure of the covering assembly to water inlet of a water tank.