Screening for Moisture: Crackle Test

One of the easiest ways to measure the presence of free and emulsified water in oil is with the hot‐plate crackle test. An emulsion is the stable state of physical coexistence of chemically insoluble substances, like oil and water. Additives and impurities that lower the oil’s surface tension can serve as agents to strengthen the emulsion. Water is in a free state when undissolved globules of water are physically suspended in the oil.

For years, oil analysis laboratories have screened samples with the crackle test, performing more detailed analysis, such as the Karl Fischer test, only when the crackle test is positive.

In the crackle test, a drop of oil is placed on a hotplate that has been heated to approximately 400°F. The sample then bubbles, spits, crackles, or pops when moisture is present. If the crackle test is negative, it simply means that the level of water present in the sample is below the detection limit; it doesn’t necessarily mean the sample is void of water.

Sometimes the crackle test may not be appropriate and you would need a Karl Fischer test done on all samples from that machine. The crackle is not a scientific test but an estimate that is affected by oil type.