Testing Coolant Solutions

A hydrometer test will indicate whether ethylene glycol and/or water should be added to maintain the desired freezing point of the solution. The freezing point of the solution should give protection to an acceptable range of -37 to -47° C (-35 to -45° F), regardless of climatic conditions. This is also necessary to provide adequate corrosion protection. Some devices used for testing solutions will indicate the correct freezing point only when tested at a specific temperature. Other testers provide thermometers and tables indicating freezing points corresponding to readings made at various temperatures. Disregarding the temperature of the solution when testing may cause an error as large as 15° C (30° F) in determining freezing points.

Due to a worldwide shortage of ethylene glycol in 1988, some coolant manufacturers have started to mix other types of glycol in the coolant formulations; propylene glycol is the most common new ingredient. A hydrometer will not always provide a correct measurement of freeze protection when anything other than ethylene glycol and water is being tested.