EP additives
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EP additives ("Extreme Pressure") are a range of organophosphates including sulfur-phosphorus and sulfur-phosphorus-boron compounds, which are used in some gear lubes and greases to provide better engine gear protection as an alternative to graphite additives.
EP gear oils perform well over a range of temperatures, speeds and gear sizes to help prevent damage to the gears during starting and stopping of the engine.
Unlike AW additives, EP additives are rarely used in motor oils. The sulfur or chlorine compounds contained in them can react with water and combustion byproducts, forming acids that facilitate corrosion of the engine parts and bearings. [1]
The early EP additives were based on lead salts of fatty acids ("lead soaps"), "active sulfur" compounds (eg. thiols and elementary sulfur), and chlorinated compounds. During 1950s the use of lead soaps was eliminated and replaced by zinc and phosphorus compounds. [2]
