Internal combustion coolant should be checked with a ______, and if the coolant is low, ______ should be added, but never add ______.

• A. hydrometer; antifreeze and/or water; alkaline water
• B. thermometer; antifreeze only; distilled water
• C. hydrometer; water only; mineral oil
• D. hydrometer; antifreeze; coffee

Answer: (A)

Testing coolant strength is done with a hydrometer because it measures the mixture’s specific gravity, which tells you the antifreeze-to-water ratio and the resulting freeze/boil protection. If the reading shows the coolant is too weak, you should add antifreeze and/or water to restore the proper mixture. Use distilled water when topping off to avoid mineral buildup. Never add alkaline water, since raising the pH can neutralize corrosion inhibitors and promote corrosion inside the cooling system. A thermometer would only indicate temperature, not the mixture, and substances like mineral oil or coffee would contaminate the system, so they’re inappropriate.