Liquid-cooled engines use distilled water and antifreeze as coolant. Newer engines use propylene glycol antifreeze, which is orange, as opposed to the more traditional green ethylene glycol antifreeze. Most engines require a mixture of half water and half antifreeze. A mixture with a higher percentage of water may freeze in cold climates, while a high percentage of antifreeze may damage the engine. A cold-check antifreeze tester -- or hydrometer -- will indicate the percentage of antifreeze in the coolant.
Shut the engine off and let it cool for at least an hour. Open the hood to facilitate the cooling process.
Remove the radiator cap or the cap on the coolant recovery tank -- depending on which system your vehicle has -- and place it aside.
Insert the hose on the hydrometer into the radiator or recovery tank so that it is submerged in coolant.
Squeeze the bulb on the hydrometer, then release it so that the body of the hydrometer fills with coolant.
Withdraw the hydrometer hose from the coolant.
Hold the hydrometer upright. Count the number of discs that are floating in the coolant mixture within the body of the tester.
Compare the number of discs floating in the coolant with the scale imprinted on the side of the tester to determine the degree of protection the coolant is providing.
Place the hose of the hydrometer back into the radiator or recovery tank opening and squeeze the bulb to expel the coolant from the tester. Replace the radiator or recovery tank cap and close the hood.
Rinse the hydrometer thoroughly with clean water after use.
