A control method for a coolant control valve unit includes detecting the coolant temperature; opening a radiator coolant supply valve; controlling the opening rate of the valve if the detected coolant temperature is higher than a target coolant temperature; and calculating a first difference value by subtracting a hysteresis value from the target coolant temperature. The blocking or controlling of the opening rate is conducted according to the detected coolant temperature and the first difference value. The hysteresis value is variable according to outside temperature.

A vehicular heat management device includes a first heat source, a second heat source, a first heat generator, a second heat generator, a heat generator pathway, a first heat source pathway, a second heat source pathway, and a switching portion. The first heat source and the second heat source heat a heat medium. The first heat generator generates heat according to operation. The second heat generator generates heat according to operation. The first heat generator and the second heat generator are provided in the heat generator pathway. The first heat generator is provided in the first heat generator pathway. The second heat generator is provided in the second heat generator pathway. The switching portion switches between a condition where the heat generator pathway is in flowing communication with the first heat generator pathway and a condition where the heat generator pathway is in flowing communication with the second heat generator pathway.

Provided is a compact boiling cooling system for an internal combustion engine that can operate in a stable manner. A lower end (4c) of a water jacket (4) of an engine (1) is connected to a lower tank (7c) of a radiator (7), and an upper end (4d) of a water jacket is connected to an upper part (7a) of the radiator. A substantially entire part of the radiator is located above the upper end of the coolant jacket so that the boiling cooling water is forwarded from the upper end of the water jacket to the upper part of the radiator, and the cooling water condensed in the radiator is forwarded from the lower end of the radiator to the lower end of the water jacket under the gravitational force without requiring a pump.

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.