Molten salt coolants are being investigated as primary coolants for a fluoride high-temperature reactor and as secondary coolants for high-temperature reactors such as the next-generation nuclear plant. This work provides a review of the thermophysical properties of candidate molten salt coolants for use as a secondary heat transfer medium from a high-temperature reactor to a processing plant. The molten salts LiF-NaF-KF, KF-ZrF4, and KCl-MgCl2 were considered for use in the secondary coolant loop. The thermophysical properties necessary to add the molten salts KF-ZrF4 and KCl-MgCl2 to RELAP5-3D were gathered for potential modeling purposes. The properties of the molten salt LiF-NaF-KF were already available in RELAP5-3D. The effect that the uncertainty in individual properties had on the Nusselt number was evaluated. This uncertainty in the Nusselt number was shown to be nearly independent of the molten salt temperature.