A transmission heat exchange system comprising: a transmission heat exchanger (103); a first valve (106), the first valve comprising at least a first coolant input and a temperature responsive component which changes condition according to its temperature; and a pump (104), the pump being arranged to pump coolant from the transmission heat exchanger to the first valve through the first coolant input. The first valve (106) is arranged to operate in a closed state and an open state according to the condition of the temperature responsive component, such that in the closed state coolant is allowed to flow from the transmission heat exchanger (103) through the first valve (106) at a first rate and in the open state coolant is allowed to flow from the transmission heat exchanger (103) through the first valve (106) at a second rate, the second rate being greater than the first rate. The temperature responsive component is at least partially immersed within the coolant in the first coolant input, and such that the condition of the temperature responsive component is at least partially determined by the temperature of the coolant within the first coolant input.