Patent ID: 8122858

Claim:
An abnormality diagnosis apparatus for a cooling system of a vehicle, which includes a coolant circuit that circulates coolant between an internal combustion engine and a radiator of the vehicle and is provided with a thermostat, wherein the thermostat is closed in a predetermined warm-up incomplete temperature range of the coolant, in which warm-up of the internal combustion engine is determined to be incomplete, to stop the circulation of the coolant between the internal combustion engine and the radiator, the abnormality diagnosis apparatus comprising: a radiator side released heat amount information obtaining means for obtaining radiator side released heat amount information, which indicates an amount of heat released from the coolant through the radiator or information relevant to the amount of heat released from the coolant through the radiator; and an abnormality diagnosis means for determining whether a thermostat open state abnormality, which is an abnormality of the thermostat that disables closing of the thermostat in the warm-up incomplete temperature range of the coolant and thereby leaves the thermostat opened in the warm-up incomplete temperature range of the coolant, exists by determining whether a predetermined thermostat abnormal time correlation exists between the radiator side released heat amount information and a vehicle speed of the vehicle in the warm-up incomplete temperature range of the coolant.