A thermostat assembly for a marine engine, having a housing with a first bore and a second bore in communication with the first bore. A thermostat mounts within the first bore for movement between an open and a closed position. A plunger removably mounts within the second bore for movement between an extended position for engagement with the thermostat, and a retracted position for disengagement with the thermostat.

A fail-safe control method for a vehicle cooling system, in which an engine and a vehicle can be properly operated even when a water temperature sensor malfunctions. When only one of two water temperature sensors malfunctions, control may be performed so that an engine and a vehicle can properly operate. When both the two water temperature sensors malfunction, the fail-safe function of the flow rate control valve can be enabled to entirely prevent cooling water from being overheated, thereby improving the reliability of the operation of the vehicle.

A main valve unit is rotatably provided in a main valve accommodation space connected to a first opening portion. A fail-safe valve unit is provided in a fail-safe valve accommodation space connected to a second opening portion. The main valve unit controls flow rate of cooling water flowing from the first opening portion to a radiator via a main water passage formed in a housing depending on a rotational position thereof. The fail-safe valve unit is closed when temperature of the cooling water is lower than a predetermined value, to thereby block off flow of the cooling water to the radiator. The fail-safe valve unit is opened when the temperature of the cooling water is higher than the predetermined value, to thereby allow the flow of the cooling water to the radiator. Each of the first opening portion and the main valve accommodation space is fluidically separated from the second opening portion and the fail-safe valve accommodation space by a partitioning wall formed in the housing.

A valve device with fail-safe mechanism capable of improved production efficiency includes a valve element, a valve element housing, a third communication port provided in the valve element housing, and a fail-safe mechanism. The fail-safe mechanism includes a thermo-element and an element housing that houses the thermo-element. The element housing, has a large-diameter housing, a small-diameter housing portion that accommodates the thermo-element, and a step. A valve element communicating portion communicating with the valve element housing is provided to the small-diameter housing portion. The fail-safe mechanism includes a valve plate member for closing the step and a coil spring that biases the valve plate member. A third adapter provided to the third communication port is provided with a through-hole that enables the large-diameter housing portion and the third communication port to communicate with each other.

A thermostat malfunction detection device that detects a stuck open state of a thermostat includes: an estimated water temperature calculation module that calculates an estimated water temperature of a cooling water based on an operation state of an engine; an actual water temperature detection unit that detects an actual water temperature of the cooling water; a first determination module that establishes preliminary determination when an amount of change of a difference between the estimated water temperature and the actual water temperature within a determined period is equal to or larger than a first threshold value; a passing air amount control module that increases a passing air amount, when the preliminary determination is established; and a second determination module that establishes malfunction determination, when the difference is equal to or larger than a second threshold value, after the passing air amount has been increased.

A refrigerant control valve apparatus includes a valve body provided with a main control valve controlling the refrigerant sent to a discharge port and a temperature sensing control valve controlling supply and discharge of the refrigerant to a temperature sensing chamber. A fail-safe mechanism is provided which supplies the refrigerant to the discharge port in a case where the temperature of the refrigerant exceeds a set value. The temperature sensing control valve is set in an open posture in a case where the main control valve is in a closed posture that closes the discharge port and the temperature sensing control valve is set in a closed posture in a case where the main control valve is in an open posture that opens the discharge port.

A thermostat is diagnosed as open failure when a specified time variation in radiator inflow water temperature from a temperature sensor mounted in a first flow path running through a radiator at a time of starting an electric water pump at a cold start of an engine is equal to or greater than a predetermined variation. In the case of open failure of the thermostat, starting the electric water pump causes cooling water from a cooling water flow path of the engine to be flowed to the first flow path, as well as to a second flow path. The radiator inflow water temperature detected by the temperature sensor mounted in the first flow path is raised by the cooling water from the cooling water flow path of the warmed engine.

An engine cooling system compromises a main channel connecting an engine and a radiator, and a coolant control valve apparatus controlling a flow rate of coolant water in the main channel having a main rotary valve. The main valve includes a rotor and a casing that has an inner peripheral surface facing an outer peripheral surface of this rotor, and a gap is provided between the outer peripheral surface of the rotor and the inner peripheral surface of the casing. The inner peripheral surface of the casing has a main opening part that is connected to the main channel, and this main opening part is provided with a sealing member that protrudes to the outer peripheral surface of the rotor. This sealing member composes a channel that connects an opening part of the rotor and an opening part of the casing.

A cooling system circulates a cooling medium between an engine and a radiator. The cooling system includes a determination unit. The determination unit sets a relatively small predetermined value for a threshold when a thermostat is closed, and sets a predetermined value larger than the predetermined value for the threshold when the thermostat is open. The determination unit determines that there is a stuck-closed failure in a selector valve when a temperature difference between a coolant temperature from a first coolant temperature sensor and a coolant temperature from a second coolant temperature sensor is larger than or equal to the threshold.

When both a position sensor and a motor malfunction, an ECU limits the engine rotation speed to such a speed range that the pressure inside a circulation route remains at or below a predetermined value even when the opening degree of a control valve is a minimum opening degree. When the position sensor is malfunction but the motor is not malfunction, the ECU relaxes the limits on the engine rotation speed, compared with when both the position sensor and the motor are malfunction, by driving the motor to an end of a motion range thereof and increasing the opening degree of the control valve to an opening degree larger than the minimum opening degree.