A vehicle thermal management system mounted in a vehicle includes a vehicle driving battery, a liquid heat transfer medium, a heat receiver, and a radiator. The heat receiver causes the heat transfer medium to receive heat through heat exchange with the battery. The radiator causes the heat transfer medium to release the heat through heat exchange with an air outside of the vehicle. The heat transfer medium includes a liquid base material including water and an orthosilicic acid ester compatible with the liquid base material and does not include an ionic rust inhibitor. The orthosilicic acid ester is present, as a concentration of silicon, relative to a total mass of the heat transfer medium within a range between 2000 mass ppm, non-inclusive, and 10000 mass ppm, inclusive.