GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC P42 Commercial Chassis 🢒 Engine 🢒 Engine Cooling 🢒 Coolant Concentration Testing

Hydrometer

Due to changes in commercially available antifreeze, the use of a hydrometer may give an incorrect reading. The hydrometer should be used in order to test an ethylene glycol-based antifreeze only. Ethylene glycol-based antifreeze (DEX-COOL™) is recommended for year round use.

Coolant Tester

Use the coolant testers J 26568 with the Centigrade scale or J 23688 with the Fahrenheit scale in order to check the antifreeze protection of the coolant. Ensure that the hydrometer markings are correct. Unless J 26568 or J 23688 has a provision for temperature correction, test the temperature at which the coolant testers are calibrated. If the coolant is warmer or colder, the reading may be incorrect. Follow the manufacturer's directions in order to use the J 26568 or the J 23688 .

Clean the coolant tester before each use with the following procedure:

  1. Swing back the plastic cover at the slanted end of the tester in order to expose the measuring window and the bottom of the plastic cover.

    2. Object Number: 13712 Size: SH
  2. Wipe the coolant tester dry with a tissue or a clean soft cloth.
  3. Close the plastic cover.

Testing

Do not remove the clear plastic pump from the tester. Use the following procedure to test the coolant:

  1. Release the tip of the pump from the tester housing.

    2. Object Number: 13709 Size: SH
  2. Insert the tip into the radiator filler neck. Insert the tip below the level of the coolant.
  3. Press and release the bulb in order to draw a sample.
  4. Bend the plastic tube around and insert the tip into the cover plate opening.
  5. Press the bulb and inject a few drops of the coolant into the measuring surface. Do not open the plastic cover when you take the readings because water evaporation may change the reading.

Reading
Object Number: 13713 Size: SH
    • Point the tester toward any light source and look into the eyepiece.
    • The antifreeze protection reading is at the point where the dividing line between the light and the dark edge of the shadow crosses the scale. The antifreeze protection is the right scale and the battery charge is on the left.
    • The tester temperature scale is reversed from the standard thermometer scale in that below zero readings are on the upper half of the scale. Readings on the lower half of the scale, which are the above zero readings, indicate solutions without enough antifreeze concentration to provide adequate rust protection.
    • Tilt the tester toward the light source in order to obtain the best results. If the edge of the shadow is not defined, the measuring surfaces are not clean or dry. Wipe the tester dry and re-test the coolant.