Diagnostic method for vehicle cooling system and diagnostic device for vehicle cooling system

A diagnostic method for a vehicle cooling system for a vehicle where a high-power unit is mounted, wherein the vehicle cooling system includes a first cooling system including a main passage structured to allow a first coolant to circulate through the main passage, wherein the high-power unit is structured to be cooled by the first coolant, wherein the first cooling system includes:

• a radiator structured to perform heat exchange with the first coolant;
• a bypass passage connected to the main passage so as to bypass the radiator;
• and a bypass valve structured to control a flow rate of the first coolant flowing through the bypass passage, the diagnostic method comprising:
• in response to a condition that a heat quantity transferred from the high-power unit to the first coolant after a startup of the vehicle cooling system has reached a predetermined value:
• receiving, by a controller, a first temperature of the first coolant at a location downstream of the radiator and upstream of a downstream end of the bypass passage in a direction of flow of the first coolant;
• calculating, by the controller, a second temperature of the first coolant based on the heat quantity;
• and
• diagnosing, by the controller, based on the first temperature and the second temperature, whether the bypass valve is in a state allowing the first coolant to flow to the radiator, or in a state preventing the first coolant from flowing to the radiator.

A vehicle cooling system diagnostic device for a vehicle where a high-power unit is mounted, the vehicle cooling system diagnostic device comprising:

• a first cooling system structured to cool the high-power unit with a first coolant, wherein the first cooling system includes:
• a main passage structured to allow the first coolant to circulate through the main passage;
• a radiator structured to perform heat exchange with the first coolant;
• a bypass passage connected to the main passage so as to bypass the radiator;
• and a bypass valve structured to control a flow rate of the first coolant flowing through the bypass passage;
• and
• a controller configured to diagnose, based on a first temperature and a second temperature, whether the bypass valve is in a state allowing the first coolant to flow to the radiator, or in a state preventing the first coolant from flowing to the radiator, wherein the first temperature is a temperature of the first coolant at a first location of the main passage downstream of the radiator and upstream of a downstream end of the bypass passage in a direction of flow of the first coolant, and wherein the second temperature is a temperature of the first coolant at a second location of the main passage downstream of the downstream end of the bypass passage and upstream of the high-power unit in the direction of flow of the first coolant.