Liquid filter, in particular an oil filter for cleaning lubricating oil for the combustion engines of motor vehicles, comprising: - a filter housing cover delimiting a housing space, in which filter housing cover a ring filter element is arranged, - at least one intermediate piece which is arranged below the filter housing cover and above the housing, when the filter housing cover is screwed onto a housing, - an inlet channel arranged on the housing side, wherein the inlet channel communicates with a dirty side of the ring filter element, and an outlet channel arranged on the housing side, wherein the outlet channel communicates with a clean side of the ring filter element, - a drainage channel on the housing side, through which the housing space can be emptied on removing the filter housing cover, - a closure mechanism arranged in the intermediate piece to be rotatable about the filter axis, which closure mechanism has a closure element for closing the drainage channel, - wherein the closure mechanism is configured such that when the filter housing cover is screwed onto the housing it is fixed in a precisely defined rotational angle position in which the closure element is arranged in alignment with the drainage channel and can be adjusted by screwing the filter housing cover into a position closing the drainage channel, whilst on unscrewing the filter housing cover the closure mechanism rotates and at the same time is moved axially away from the housing so that the closure element releases the drainage channel, characterised in that the closure mechanism is configured as a spring plate, which comprises a ramp-like mandrel, which projects axially in the direction of the housing, and comprises at least three flexible cantilever arms (22a, 22b, 22c), which project in the direction of the ring filter element and are arranged on a circumferential path. - a filter housing cover delimiting a housing space, in which filter housing cover a ring filter element is arranged, - at least one intermediate piece which is arranged below the filter housing cover and above the housing, when the filter housing cover is screwed onto a housing, - an inlet channel arranged on the housing side, wherein the inlet channel communicates with a dirty side of the ring filter element, and an outlet channel arranged on the housing side, wherein the outlet channel communicates with a clean side of the ring filter element, - a drainage channel on the housing side, through which the housing space can be emptied on removing the filter housing cover, - a closure mechanism arranged in the intermediate piece to be rotatable about the filter axis, which closure mechanism has a closure element for closing the drainage channel, - wherein the closure mechanism is configured such that when the filter housing cover is screwed onto the housing it is fixed in a precisely defined rotational angle position in which the closure element is arranged in alignment with the drainage channel and can be adjusted by screwing the filter housing cover into a position closing the drainage channel, whilst on unscrewing the filter housing cover the closure mechanism rotates and at the same time is moved axially away from the housing so that the closure element releases the drainage channel, characterised in that the closure mechanism is configured as a spring plate, which comprises a ramp-like mandrel, which projects axially in the direction of the housing, and comprises at least three flexible cantilever arms (22a, 22b, 22c), which project in the direction of the ring filter element and are arranged on a circumferential path.