GM Service Manual Online
For 1990-2009 cars only

Tools Required

    • J 23688 Coolant Tester (Fahrenheit Scale)
    • J 26568 Coolant Tester (Celsius Scale)
    • Hydrometer (for Dex-Cool® antifreeze concentration only)
    • Refractometer

Object Number: 1392  Size: SH

Important: Use a hydrometer in order to test Dex-Cool® antifreeze concentration only. Other solutions may not provide a correct reading. Dex-Cool® antifreeze is recommended for use around the year. A refractometer also tests the antifreeze protection level. Unless the refractometer has a provision for temperature correction, test at the temperature for which the refractometer has been calibrated. If the coolant is warmer or cooler, the reading may be incorrect. Follow the manufacturer's directions exactly.

  1. Before each use of the J 23688 or J 26568 coolant tester, perform the following steps:
  2. 1.1. Swing back the plastic cover at the slanted end of the J 23688 or J 26568 coolant tester in order to expose the measuring window and the bottom of the plastic cover.
    1.2. Wipe the measuring window dry using a tissue or a clean, soft cloth.
    1.3. Close the plastic cover.

    Do not remove the clear plastic cap from the tester.


    Object Number: 1393  Size: SH
  3. Insert the tip of the sample tube into the radiator filler neck.
  4. Submerge the sample tube into the coolant solution.
  5. Press and release the pump bulb in order to obtain a sample.
  6. Insert the tip of the sample tube into the cover plate opening of the J 23688 or J 26568 .
  7. Press the pump bulb in order to inject a few drops of coolant onto the measuring surface.
  8. Do not open the plastic cover. Water evaporation will affect the reading.


    Object Number: 6349  Size: SH
  9. Point the J 23688 or J 26568 coolant concentration tester toward any light source. Look into the eyepiece.
  10. • 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.
    • Readings on the lower half of the scale indicate solutions without enough protection.
    • If the readings are not clear, the measuring surfaces were not cleaned and dried properly. Wipe dry and conduct a new test.
    • Adjust the coolant protection level as necessary.