A controllable mechanical motor vehicle coolant pump comprising - a rotatable drive shaft which extends in an axial pump direction and is configured to be mechanically driven by an engine of a motor vehicle, - a coolant pump wheel which is co-rotatably connected with the drive shaft and is configured to pump a liquid coolant, - a transverse housing surface which extends substantially transversely with respect to the drive shaft and radially surrounds the drive shaft, - a cylindrical inner slider support surface which radially surrounds the drive shaft and is coaxial to the drive shaft, characterised in that the coolant pump further comprises: - a substantially pot-shaped control slider which is configured to be axially shiftable with respect to the coolant pump wheel in order to control an effective discharge flow cross-section (D-eff) of the coolant pump wheel, the control slider comprising • a substantially cylindrical slider side wall which is configured to radially surround the coolant pump wheel, and • a slider bottom wall which extends substantially transversely with respect to the drive shaft and is arranged axially between the coolant pump wheel and the transverse housing surface, wherein a radially inner bottom wall surface of the slider bottom wall is shiftably supported by the inner slider support surface, and - a push-out pressure chamber which • is located between the slider bottom wall and the transverse housing surface, • is defined at one axial side by the transverse housing surface and radially inwardly by the inner slider support surface, and • is configured to be hydraulically pressurized in order to generate a hydraulic push-out push force which pushes the slider bottom wall toward the coolant pump wheel, wherein the transverse housing surface and the inner slider support surface are both defined by a first housing element. - a rotatable drive shaft which extends in an axial pump direction and is configured to be mechanically driven by an engine of a motor vehicle, - a coolant pump wheel which is co-rotatably connected with the drive shaft and is configured to pump a liquid coolant, - a transverse housing surface which extends substantially transversely with respect to the drive shaft and radially surrounds the drive shaft, - a cylindrical inner slider support surface which radially surrounds the drive shaft and is coaxial to the drive shaft, - a substantially pot-shaped control slider which is configured to be axially shiftable with respect to the coolant pump wheel in order to control an effective discharge flow cross-section (D-eff) of the coolant pump wheel, the control slider comprising • a substantially cylindrical slider side wall which is configured to radially surround the coolant pump wheel, and • a slider bottom wall which extends substantially transversely with respect to the drive shaft and is arranged axially between the coolant pump wheel and the transverse housing surface, wherein a radially inner bottom wall surface of the slider bottom wall is shiftably supported by the inner slider support surface, and • a substantially cylindrical slider side wall which is configured to radially surround the coolant pump wheel, and • a slider bottom wall which extends substantially transversely with respect to the drive shaft and is arranged axially between the coolant pump wheel and the transverse housing surface, wherein a radially inner bottom wall surface of the slider bottom wall is shiftably supported by the inner slider support surface, and - a push-out pressure chamber which • is located between the slider bottom wall and the transverse housing surface, • is defined at one axial side by the transverse housing surface and radially inwardly by the inner slider support surface, and • is configured to be hydraulically pressurized in order to generate a hydraulic push-out push force which pushes the slider bottom wall toward the coolant pump wheel, wherein the transverse housing surface and the inner slider support surface are both defined by a first housing element. • is located between the slider bottom wall and the transverse housing surface, • is defined at one axial side by the transverse housing surface and radially inwardly by the inner slider support surface, and • is configured to be hydraulically pressurized in order to generate a hydraulic push-out push force which pushes the slider bottom wall toward the coolant pump wheel,