In an effort to communicate the limitations of the crackle test in detecting water contamination, TestOil embarked on a lab study to uncover crackle detection limits. A total of 493 samples comprised of a variety of lubricant types were run on a 400°F hot plate. The samples were assessed for a positive or negative crackle. These same samples were then analyzed for water contamination using a Karl Fischer titration (ASTM D6304‐C). The water results were recorded in parts per million (ppm). The table below summarizes the results of the study. The table lists oil type, the number of samples in the study, the detection limit range, the lowest negative crackle value, and the highest positive crackle value.

The lowest positive values represent those samples that exhibited a positive crackle and the associated Karl Fischer result while the highest negative values represent those samples that clearly had water present according to the Karl Fischer results, yet didn’t crackle. Clearly, the study demonstrates that quite a bit of variance exists in the water detection limit of the crackle test. You really need to know your lubricant type before making assumptions on what the crackle can detect. In some cases, your water limits may fall below crackle detection and running the Karl Fischer test on every sample may be worth the cost.