What are "Copper Corrosion" values and when to worry about them?

 

The "Copper Corrosion" rating is a classification (such as 1A, 1B, 2A, 2B, etc.) that indicates the amount of free or active sulfur present in a lubricant. The higher the sulfur content, the greater the lubricant’s Extreme Pressure (EP) performance, as free sulfur forms a protective sacrificial layer on metal surfaces, shielding the metal underneath.

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However, there is a drawback: lubricants with free sulfur should not be used in applications involving yellow metals (like brass or bronze) because the sulfur can cause corrosion to these metals.