Bypass valve for a cooler arranged downstream of a hydraulic unit

The invention relates to a bypass valve for a downstream a hydraulic aggregate cooler, comprising a valve housing (2) with connection openings (8, 12, 18) for connection with the hydraulic unit on the one hand and the cooler on the other hand, a valve disposed in the valve housing closure member (22) having a bypass includes, or in the closed position opens a the closure element (22) urging the valve spring (32), and thermosensitive means which temperature of the hydraulic fluid located at a below a predetermined threshold temperature (about 80 ° C) cause opening of the closure element (22). According to the invention it is provided that the heat-sensitive means by the valve spring (32) themselves are formed, which is formed for this purpose from a memory metal alloy with a lying at the threshold temperature transition point such that it is powerless below this threshold temperature and opening of the closure element (22) to allow, under the effect of hydraulic fluid pressure. In this way, different thermosensitive means, such as a temperature-controlled actuator omitted.