Cloud Point and Pour Point:

When the lubricant oil is cooled slowly, the  temperature at which it becomes cloudy or hazy in appearance, is called its cloud point; while the temperature at which the lubricant oil cease to flow or pour, is called its pour point. Cloud and pour points indicate the suitability of lubricant oil in cold conditions. Lubricant oil used in a machine working at low temperatures should possess low pour point; otherwise solidification of lubricant oil will cause jamming of machine. It has been found that presence of waxes in the lubricant oil raise pour point. The lubricating oils are derivatives of petroleum and contain dissolved paraffin wax and other resinous impurities. These impurities tend to separate from the oil at lower temperatures. The solidification of lubricant causes jamming of machines. “The temperature at which the impurities begin to separate from the solution and lubricating oil becomes cloudy or hazy in appearance is called cloud point” “The cloud point is the temperature at which crystallization of solids in the form of cloud or haze first becomes noticeable, when the oil is cooled at a standard rate."

Significance:

• The cloud point indicate stability of lubricants in cold conditions.
• Cloud point is useful for estimating the temperature at which

Filter screens in the fuel intake system of diesel engine clogged because of separation of wax.It is useful to understand the stability of lubricants in cold conditions. “The pour point is the temperature at which the oil just ceases to flow when cooled at a standard apparatus. “OR  “The temperature at which the lubricating oil ceases to flow and pour is called pour point”

Significance:

• It indicates the stability of lubricants in cold conditions
• Pour point values of petroleum and non-petroleum lubricants are necessary when functioning under sub-freezing conditions.
• It determines suitability of lubricant or hydraulic oil for low temperature installations.