This disclosure details thermal management systems for thermally managing electrified vehicle battery packs. An exemplary battery thermal management system may monitor the availability and effectiveness of a radiator for thermally managing a battery pack. A control unit may be configured to actuate a valve from an open position to a closed position that prevents the flow of the coolant to the radiator when a coolant temperature of the coolant exceeds a modified ambient temperature. The modified ambient temperature may be derived as a function of a vehicle speed.