Cold-Chek® Professional Anti-Freeze Tester. Large professional-size (16 1/4”) tester is accurate at all temperatures. Tests coolant, hot or cold. Celsius and Fahrenheit scales. Special feature is the “6th disc” which shows over protection and a loss of cooling efficiency. Beyond 70% antifreeze, cooling & corrosion effectiveness is reduced. Tests Dex-Cool, Prestone, Zerex, and long-life coolants.