Which instrument is utilized to accurately check antifreeze protection in a heavy-duty diesel engine?

The refractometer is the instrument specifically designed to accurately check antifreeze protection in a heavy-duty diesel engine. This device measures the refractive index of the antifreeze solution, which correlates to the concentration of ethylene glycol or propylene glycol in the mixture. By determining the refractive index, the refractometer provides an indication of the freezing point of the coolant, thereby allowing technicians to assess whether the antifreeze provides adequate protection against low temperatures.

In contrast, while a hydrometer measures the specific gravity of liquids, it is less accurate for assessing antifreeze concentrations as it does not directly measure the refractive properties. A thermometer simply measures temperature, providing no information about the antifreeze concentration or its protective qualities. A pneumatic gauge measures pressure, which is unrelated to the antifreeze protection level in the engine. Therefore, the effectiveness of the refractometer in evaluating antifreeze protection makes it the most suitable choice for this purpose.