A transmission fluid circuit for regulating the flow of a fluid includes a transmission, a cooler, and a valve. The valve includes a housing, a spool, and an actuator including a smart material. The spool is movable inside the housing between a first position and a second position. The smart material is configured to be in an activated state in response to the fluid exhibiting at least a first temperature and to be in a deactivated state in response to the fluid being a sufficient number of degrees less than the first temperature. The fluid flows from the housing to the transmission and from the transmission to the housing when the spool is in the first position. The fluid flows from the housing to the cooler, from the cooler to the transmission, and from the transmission to the housing when the spool is in the second position.