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‘Low SAPS’ engine oil technologies: Low SAPS technologies are being introduced primarily in markets with both a high-diesel population and high-quality diesel fuel. Legislators in markets with high-diesel populations have driven diesel fuel quality to higher levels. That same legislation is now driving reduced tailpipe emissions via after-treatment devices such as diesel particulate filters. These filters can be blocked by metallic ash formed from oil burned during the combustion process.
As a consequence of the introduction of DPFs, modern formulations are now using less of traditional ash-containing components. Ash for oils is measured by a standard method known as ‘Sulphated Ash’ via the ASTM D874 procedure. The main changes between full SAPS and mid/low SAPS formulations are described below.
The use of metal-containing additives is becoming restricted, with knock-on effects over the whole lubricant formulation. Using ash-containing detergents such as the overbased calcium and magnesium salts of sulphonates, phenates and salicylates
is now restricted by their ash content. With restrictions on the amount of ash-forming components, a balance has to be struck between detergents and the amount of ZDDP antiwear, which also contains ash. ZDDP also has a major effect on the lubricant’s phosphorus and sulphur content.
In a typical full SAPS additive package there is a higher combination of the detergent and ZDDP which can result in higher Sulphated Ash when the oil is burned. In Low SAPS oils these are traded out for a higher concentration of ashless dispersants and newer detergents that work without high levels of calcium or magnesium salts. The same is true with the antiwear additives and ZDDP - reduced ZDDP means increase in the effectiveness of other friction modifiers and antiwear additives. (this is why the VOA of a diesel engine oil meeting CJ-4 will show lower levels of these elements vs one that meets SN).
Many of these oils are also cross compatible meaning they meet both the Service and Commercial category requirements.
So to answer the original question:
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Is this true? Does higher ash content act as lubricant?
no it has nothing to do with lubrication and everything to do with detergency.
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If ash is not a lubricant, should i use 507 oil in a VW gasoline engine for the pure benefit of low ash?
Depending on the gasoline engine type and if the oil in question also meets SM or SN I see no issues. However I would typically recommend using a gasoline rated oil for a gasoline engine and a diesel oil for a diesel engine.