Patent ID: 7409929

Claim:
A cooling apparatus for an internal combustion engine, comprising: a thermostat that adjusts a feed rate of a coolant to a radiator; a detecting device that detects a temperature of said coolant; an estimating device that estimates a reference temperature equivalent to the temperature of said coolant at least based on a detection value of an intake-air temperature sensor; and a diagnosis device that sets the temperature of said coolant detected by said detecting device to a detection temperature, and diagnoses an operating state of said thermostat by comparing said detection temperature and said reference temperature when a predetermined diagnosis condition is established, wherein a state in which a difference between the detection value of said intake-air temperature sensor and an external air temperature is equal to or greater than an upper limit value is set to a specific state, and wherein the diagnosis of said operating state is prohibited when a first time period of said specific state is equal to or longer than an upper limit time period, the upper limit time period being a period of time before the establishment of said diagnosis condition.