Cooling device anomaly diagnosing apparatus

A cooling device anomaly diagnosing apparatus adapted for a cooling device in an internal combustion engine, wherein the cooling device includes an inner channel serving as a cooling channel located inside the internal combustion engine, an outer channel serving as a cooling channel located outside the internal combustion engine, the outer channel constituting, together with the inner channel, a loop path in which cooling water is circulated, and a multi-port valve capable of adjusting a cross-sectional area of a flow passage between the inner channel and the outer channel by an electronic control, the multi-port valve including a check valve configured to open when a pressure inside is higher than a pressure in the outer channel by an amount greater than or equal to a predetermined amount, the anomaly diagnosing apparatus is configured to execute an enlarging process of enlarging the cross-sectional area of the flow passage by operating the multi-port valve such that the cross-sectional area is larger in a case where a rotational speed of a crankshaft of the internal combustion engine is at a predetermined speed or higher than in a case where the rotational speed is lower than the predetermined speed, a rate calculating process of calculating, within a predetermined time period after startup of the internal combustion engine, a reference rate such that the reference rate has a larger value in a case where a fuel injection amount of the internal combustion engine is large than in a case where the fuel injection amount is small, the reference rate being a reference value for a rate of rise of a cooling water temperature in sections of the loop path other than the outer channel, and an anomaly determining process of determining, within the predetermined time period, that an anomaly is present in the check valve if a rate of rise of a detection value of a cooling water temperature in paths other than the outer channel is smaller than the reference rate, and a notifying process to prompt a user if an anomaly is determined to be present in the check valve, wherein the rate calculating process includes calculating the reference rate such that the reference value has a smaller value in a case where the enlarging process is executed than in a case where the enlarging process is not executed.