Thermally responsive bypass valve

A bypass valve 105 has a bypass block 330 defining a bypass flowpath 301, 302 communicating with main flowpaths 220, 221. A member 400 is disposed within the bypass block to move between first and second positions that respectively allow and block fluid flow through the bypass flowpath. An elastic element 500 is coupled to the member 400 and biases the member toward the fluid blocking position responsive to a temperature of fluid flowing along the main flowpaths 220, 221. The elastic element 500 is a memory metal alloy spring and a carbon steel spring 502 applies a restorative bias to the member 400.