Some coolant manufacturers mix other types of glycol into their coolant formulations. Propylene glycol is the most common new ingredient.

A hydrometer does not always provide a correct measurement of freeze protection when anything other than ethylene glycol and water is being tested. The degree of inaccuracy varies depending on the proportion of other glycols present in the coolant.

All new GM vehicles are produced with coolant that can be accurately measured with a hydrometer; however, when the type and quality of coolant being measured is unknown, such as a customer vehicle that has accumulated mileage, the use of a refractometer is recommended.

Coolant testers J 26568 (Centigrade Scale) or J 23688 (Fahrenheit Scale) can be used to check the antifreeze protection of the coolant. Make sure the refractometer markings are correct. Unless J 26568 or J 23688 has a provision for temperature correction, test the temperature at which J 26568 or J 23688 is calibrated. If the coolant is warmer or cooler, the reading may be incorrect. Follow the manufacturers' directions on using J 26568 or J 23688 .

Tools Required

Important: 

•	Before each use, swing back the plastic cover at the slanted end of the coolant tester, exposing the measuring window and the bottom of the plastic cover.

•	Wipe the measuring window dry with a tissue or a clean, soft cloth.

•	Close the plastic cover.

•	Do not remove the clear plastic pump from the J 23688 or the J 26568 .

1. Release the tip of the pump from the housing of the J 23688 or the J 26568 .



2. Insert the tip of the pump into the radiator filler neck. The tip of the pump must be below the level of the coolant.
3. Press the bulb. Release the pump bulb in order to obtain a sample of the coolant.
4. Insert the tip of the pump into the cover plate opening.
5. Press the pump bulb. Allow a few drops to fall onto the measuring surface. Do not open the plastic cover when taking readings because any water evaporation will change the reading.



6. Point the coolant concentration tester toward any light source. Look into the eyepiece.

•	The coolant protection reading is at the point where the dividing line between light and dark crosses the scale. Antifreeze protection is the scale on the right.

•	The temperature scale is reversed from a standard thermometer scale. Below zero readings are on the upper half of the scale.




7. If the readings are not clear, properly clean and dry the measuring surface. Conduct a new test.