As oil cools to 40° F and below, waxes in the oil will crystallize. As the oil is cooled further to freezing or below, moisture in the oil will form ice. The temperature at which these crystals form and are visible is called the Cloud Point. The greater the quantity of wax present, the higher the cloud point. Wax crystals have a different appearance than ice crystals and will form above 32° F.
If you continue to chill the oil, eventually the oil will not flow out of the test tube when turned upside down. The temperature at which this occurs is call the Pour Point. These tests are conducted by simply chilling the oil and observing at what temperature this occurs.
The Cloud and Pour Point characteristics of an oil are important factors when selecting a lubricant for chiller applications, oil mist applications, and in Northern regions where temperatures routinely reach 0° F in the winter time.
The Cloud Point and Pour Point tests should not be a part of your routine analysis program. It is a quality check of the lubricant and should be performed for evaluation of new oils or when a wax problem is apparent or suspected in the system.