Which instrument is used to check the level or condition of engine coolant in an internal combustion engine?

• A. Hydrometer
• B. Thermometer
• C. Barometer
• D. Hygrometer

Answer: (A)

Focus: coolant concentration. A hydrometer measures the density (specific gravity) of the coolant mixture, which tells you the ratio of antifreeze to water. This directly indicates the coolant’s protection level against freezing and boiling, as well as whether additives are still effective. If the concentration is too low, the coolant may need topping up or replacement; if too high, you might have over-concentration that can reduce heat transfer. The other instruments measure things the coolant isn’t about here: a thermometer only shows temperature, a barometer measures atmospheric pressure, and a hygrometer gauges humidity. So the hydrometer is the tool used to assess the level/condition of engine coolant.