Methods and systems are provided for a cooling system valve comprising a fusible insert and a heating element coupled to the insert. In one example, in response to an increase in coolant temperature to above a first threshold temperature, a movable element of the cooling system valve may be actuated to a fully open position and in response to an increase in coolant temperature to above a second threshold temperature with the movable element in a fully open position, electric current may be routed through the heating element to heat and melt the fusible insert. By melting the fusible portion, coolant may flow through an opening created in the movable element.

A failure diagnosis method of a coolant temperature sensor for a vehicle, may include determining, by a controller, whether or not it is in a flow stop state that stagnates the flow of coolant by a flow control valve; obtaining, by the controller, an engine outlet coolant model temperature when it is in the flow stop state; and diagnosing, by the controller, as a failure of an engine outlet-side outlet water temperature sensor when the coolant model temperature is equal to or greater than a reference temperature and the flow stop state is maintained by the flow control valve.

A control method for a cooling system is provided. The method includes determining whether the output signals of a first coolant temperature sensor and a second coolant temperature sensor satisfy a predetermined coolant overheating condition. A coolant control valve unit is operated to move the cam to a maximum position when the predetermined coolant overheating condition is satisfied. Additionally, a control temperature is determined according to an output signal of the first coolant temperature sensor and the second coolant temperature sensor and an operation of the injector is limited according to the determined control temperature.

A control method of a coolant control valve unit that rotates a cam using torque of a motor and allowing a profile formed on the cam to push a rod to allow the valve formed on the rod to open/close a coolant passage, including steps of: rotating the cam by operating the motor; detecting a rotation position of the cam; determining a stuck state in which the cam or the motor is not rotated while the motor is operated; and performing an escape mode in which if it is determined that the cam or the motor is in the stuck state, the motor outputs a predetermined torque to the cam side in a predetermined rotation direction to escape the cam from the stuck state.

A thermostat misdiagnosis prevention method applied to an engine system of the present disclosure applies high speed/high load and low speed/low load, which are divided by a vehicle speed and an engine output detected from the engine system at an engine warm-up temperature of engine coolant, as monitoring conditions of a thermostat, and determines thermostat fail by primarily determining the thermostat fail with the engine coolant temperature of the engine coolant temperature and the outside air temperature detected from the engine system, then confirming a delay time with respect to the outside air temperature, and secondarily determining the thermostat fail with the engine coolant temperature in a monitoring ECU, thereby corresponding to the enhanced OBD together with preventing the misdiagnosis of the thermostat by the fail-safe according to the primary and secondary determinations.

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 thermostat includes: a thermostat housing having an inlet and an outlet; an internal housing having a main valve hole and a fail-safe hole, wherein the internal housing is disposed within the thermostat housing and internal housing and has a main chamber communicating with the inlet of the thermostat housing; a wax housing disposed within the internal housing and having a first wax and a second wax; a first valve selectively opening or closing the main valve hole according to expansion or shrink of the first wax; and a second valve selectively opening or closing the fail-safe hole according to expansion or shrink of the second wax.

A control method for a cooling system is provided. The method includes determining whether the output signals of a first coolant temperature sensor and a second coolant temperature sensor satisfy a predetermined coolant overheating condition. A coolant control valve unit is operated to move the cam to a maximum position when the predetermined coolant overheating condition is satisfied. Additionally, a control temperature is determined according to an output signal of the first coolant temperature sensor and the second coolant temperature sensor and an operation of the injector is limited according to the determined control temperature.

An ECU that is a diagnostic device includes a calculation unit that is a water temperature obtaining unit obtaining the temperature of a discharge coolant which is a coolant discharged from an engine, a diagnostic unit that diagnoses a thermostat which is a temperature adjusting valve by comparing the temperature of the discharge coolant and a threshold, and a suspending unit that suspends a diagnosis performed by the diagnostic unit. The suspending unit suspends a diagnosis performed by the diagnostic unit in a case where the temperature of the discharge coolant is estimated to be lower than the threshold according to an operating condition of the vehicle even though the thermostat is normal.

A vehicle includes: a radiator that cools cooling water; a grille shutter that is provided on a vehicle front side of the radiator and opens or closes a grille provided in a vehicle; a first flow path in which the cooling water passes through the radiator; a second flow path in which the cooling water does not pass through the radiator; a thermostat that switches a path between the first flow path and the second flow path; and a failure determiner that performs failure determination of the thermostat based on an actual temperature of the cooling water and an estimated temperature of the cooling water, the estimated temperature being calculated based on a temperature change of the cooling water caused by an open or close state of the grille shutter.