Home » GM 6.5 » GM/Detroit 6.5L – COOLANT DIAGNOSIS


Due to changes in commercially available antifreeze, the use of a hydrometer may give an incorrect reading. The hydrometer should be used to test ethylene glycol base an tifreeze only. Ethylene glycol base antifreeze is recommended for year round use.

Coolant testers J 26568 (Centigrade Scale) and J 236 88 (Fahrenheit Scale) can be used to check the
anti-freeze protection of the coolant. Make sure the hydrometer readings are correct. Unless J 26568 or J 23688 has a provision for temperature correction, test the tem perature at which J 26568 or J 23688 is calibrat­ed. If the coolant is w arm er or cooler, the reading may be incorrect. Follow the manufacturer’s directions for using J 26568 or J 23688.

• Before each use, swing the plastic cover back at the slanted end of J 26568 or J 23688, exposing the measuring window and the bottom of the plastic cover (figure 2).
• Wipe dry with tissue or clean soft cloth.
• Close the plastic cover.

Tools Required:
J 26568 or J 23688 Coolant Tester
• Do not remove the clear plastic pump from the tester.

1. Release the tip of the pump from J 26568 or J 23688.
2. Insert the tip of the pump into the radiator filler neck (figure 3).
3. Make sure the tip of the pump is below the level of the coolant.
4. Press and release the bulb to draw a sample.
5. Insert the tip of the pump into the cover plate open­ing.
6. Press the bulb and inject a few drops of coolant onto the measuring surface.
• Do not open the plastic cover when taking readings because water evaporation can change the reading.

• Point J 26568 or J 23688 toward any light source and look into the eyepiece (figure 4).
• 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).
• Temperature scale is reversed from a standard thermometer scale.
• Below zero readings are on upper half of the scale.
• Readings on the lower half of the scale indicate solutions without enough antifreeze concentra­tion to provide adequate rust protection.
• If the readings are not clear, the measuring sur­ faces were not cleaned and dried properly.
Wipe dry and make a new test.


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