LO 11-8 Outline maintenance procedures and identify tools and methods used to perform maintenance on a diesel engine cooling system

Measuring Freeze Protection

The use of a hydrometer or refractometer is necessary when testing the freeze protection of the coolant in the cooling system. The customer may request this service as part of a winterization package performed by the workshop. Any time coolant is replaced in the cooling system, the freeze point should be verified after the coolant has circulated.

The hydrometer is a tool that measures the specific gravity of a liquid. When coolant is drawn into the hydrometer, a float rises to a specific level depending upon the density of the coolant. Antifreeze has a higher specific gravity than water, so the higher the float rises in the liquid, the greater the percentage of antifreeze in the mix. One drawback to hydrometers is that they are typically antifreeze specific. This means a different one may be needed to check both ethylene glycol and propylene glycol because the specific gravities of the two base liquids are different. Another drawback is that as the temperature of the coolant goes up, the specific gravity goes down. Some hydrometers have a built-in thermometer and a chart, enabling a technician to apply a correct factor for the temperature of the coolant.

A refractometer can also be used to test the proportions of antifreeze and water in the coolant mix (or the level of freeze protection) by measuring a liquid’s specific gravity. It operates by allowing light to pass through the fluid. The light bends proportionally to the particular liquid’s specific gravity. The bending of the light displays on a scale inside the tool, indicating the specific gravity of the fluid.

To use a hydrometer to test the freeze point of the coolant, follow the steps in Skill Drill 11-5. To use a refractometer to test the freeze point of the coolant, follow the steps in Skill Drill 11-6.