The Rhino Duo-Chek DC70 measures both Ethylene Glycol and Propylene Glycol based engine fluids. (Propylene Glycol is the environmentally-friendly antifreeze, which hydrometers cannot measure!) Accuracy in testing engine coolant is important to ensure adequate freeze and boil-over protection. Accurate coolant concentration also means the viscosity and heat transfer properties are correct. The proper coolant/water mix provides proper cooling system operation and prevents engine damage from cavitation corrosion.