Some coolant manufactures have started to mix other types of glycol in their coolant formulations. Propylene glycol is the most common new ingredient. A hydrometer will not always provide a correct measurement of freeze protection when anything other than ethylene glycol and water is being tested. The degree of inaccuracy will vary 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, 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 colder, the reading may be incorrect. Follow the manufactures directions using J 26568 or J 23688.

Important: 

Tools Required

1. Release the tip of the pump from the housing of the J 23688 or the J 26568 .
2. Do not remove the clear plastic pump from the J 23688 or the J 26568 .

Caution: As long as there is pressure in the cooling system, the temperature can be considerably higher than the boiling temperature of the solution in the radiator without causing the solution to boil. Removal of the pressure cap while the engine is hot and pressure is high will cause the solution to boil instantaneously -- possibly with explosive force -- spewing the solution over the engine, fenders and the person removing the cap.




3. Insert the tip of the pump into the filler neck of the radiator. The tip of the pump must be below the level of the coolant.
4. Press the bulb. Release the pump bulb in order to obtain a sample of the coolant.
5. Insert the tip of the pump into the cover plate opening.
6. 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.



7. 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.




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