A cooling apparatus for a dot matrix impact print head suitable for application in serial printers. The print head is mounted on a carriage sliding on guide bars for reciprocating movement thereon. A liquid filled container having an inlet and outlet is mounted on the carriage and is in thermal contact with the printing head. A heat dissipator also mounted on the printer has a liquid filled cavity with inlet and outlet with flexible conduits connected to the inlets and outlets so as to form a liquid circulation loop. A unidirectional fluid valve in said loop maintains liquid circulation in the loop by the reciprocating movement of the liquid container.
In the preferred form of embodiment the liquid container is formed integral with the print head, the liquid in the container being in direct contact with electromagnetic cores of the print head, and the heat dissipator is formed by a guiding bar, the bar being hollow and having an inlet and outlet.