GM/Detroit 6.5L – BUILT-IN HYDROMETER

Molded into the top of the maintenance-free battery is a built-in temperature compensated hydrometer (figure 4). Use this hydrometer with the following diagnostic procedure.
When observing the hydrometer, make sure the bat­tery has a clean top. A light may be required in some poorly-lit areas.
Under normal operation, one of three indications can be observed:
1. GREEN DOT VISIBLE
• Any green appearance in the hydrometer is interpreted as a “green dot.” This meams the battery is ready for testing.
2. DARK DOT, GREEN DOT NOT VISIBLE
• If the green dot cannot be seen and there is a cranking complaint, proceed to “ Diagnosis of the Battery” for further testing. The charging system should be tested for output and the electrical system should be tested for excessive draws.

3. CLEAR OR LIGHT YELLOW-DOT
• This means the electrolyte level is below the bottom of the hydrometer and is too low for diagnosis. This m ay have been caused by excessive or prolonged charging, a broken case, or excessive tipping. When finding a bat­tery in this condition it may indicate high charg­ing voltages caused by a faulty charging system. Therefore, the charging and electrical systems must be tested. The battery should be replaced if a cranking complaint exists and the battery has a yellow or clear hydrometer.

 

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