Determining Coolant Protection

A coolant hydrometer can be used to approximate the coolant's freezing protection if it is unknown. The specific gravity of the coolant is used to determine the concentration of antifreeze in the coolant and therefore the coolant's freezing point. The freezing point of coolant varies with its antifreeze concentration as indicated in the graph below.

COOLANT PROTECTION GRAPH

To determine your coolant's low temperature protection (freezing point), follow this procedure:

  1. Park the vehicle on level ground in a well-ventilated area with the engine ON, the parking brake engaged, and the transmission in PARK (for automatic) or REVERSE (for manual) . Open the hood. Bring the engine up to operating temperature with the radiator cap removed and engine idling. The upper radiator hose should be hot.
  2. Use the hydrometer to draw a fluid sample from the radiator and read the temperature. Pour the sample back into radiator and repeat this process until there is no further change in the temperature reading. However, try to avoid a boilover since the system is not pressurized.
  3. Pull one last coolant sample from the radiator and read the letter on the hydrometer float scale. Be sure the hydrometer float does not rub against the sides of the sample tube.
  4. Use the chart that accompanies the hydrometer to convert the letter reading on the float scale to a coolant freezing point.
  5. If the low temperature protection is inadequate, adjust the coolant mixture as indicated in Modifying Coolant Protection. To adjust the coolant mixture, it will be necessary to drain some coolant and replace it with pure antifreeze.
  6. After adjusting the coolant mix, warm-up the engine and check the freezing point again using a hydrometer.

A coolant's boiling point will change slightly with a variation in antifreeze concentration. The cooling system relies mostly on pressure buildup, not antifreeze concentration, to raise the coolant boiling point substantially.


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