"We notice a different color in the lubricants we get from our lubricant supplier in each shipment of the same product. Sometimes the oil is lighter colored, cloudy, darker, etc. Is this a problem?"
For Group I mineral oils, slight changes in color or darkness often occur due to differences in crude stock. Color bodies in mineral oils are generally associated with sulfur or aromatic impurities. The darker the base oil, the more of these impurities you usually find. Dark color is more pronounced in higher viscosity mineral oils.
Certain additives also contribute to color, especially those containing sulfur. For instance, detergents such as calcium sulfonate can substantially darken a finished oil. If your lubricant supplier has made a formulation change, this can lead to a corresponding color change. Most responsible lubricant suppliers disclose planned formulation changes to their customers in advance.
Regardless of the color, with few exceptions, a new oil should be clear and bright. If your oil is normally clear and bright, but a new delivery reveals a cloudy appearance, this is generally a cause of concern. Reasons for this can vary, but those on the list below are common:
1. Insoluble additives (blend plant or storage stability problems)
2. Water contamination
3. Accidental cross-mixing of lubricant types where additives or base oils have clashed
4. Solid impurities
5. Low cloud point (wax crystallization)
When in doubt, retain a sample of the oil and have it analyzed.