Abstract: The disclosure relates to an electric machine cooling system comprising a cooling cartridge arranged inside and coaxial to an inner hollow shaft of an inner rotor. The cooling cartridge is a polymer cartridge that is interchangeably attached to the inner rotor. The cooling cartridge includes an inner coolant tube having an internal coolant duct configured to lead coolant from an inlet opening of the inner coolant tube to a closed dead-end of the cooling cartridge, and an outer coolant sleeve comprising coolant channels which are fluidically connected with the internal coolant duct via at least one connection channel and which are configured to lead the coolant from the at least one connection channel to at least one outlet opening.