- Joined
- Feb 11, 2021
- Messages
- 80
I always understood the SAPS thing as the higher the SAPS the higher the TBN to deal with higher-sulfur fuels over the typical drain intervals here in the U.S. vs. Europe that has v. low sulfur fuels and could get away with lower SAPS oils for long-service intervals. In my world, this is the difference between VW502 00 oils (high SAPS) vs. VW504 00 oils (mid or low[?] SAPS).
With the demise of Group I, solvent extracted base oils in engine oils, there's really no sulphur contribution from base oil anymore. In modern Group IIs & synthetics, the 'S' & 'P' simply reflect how much ZDDP you have in the oil. Yes you will get some Sulphur from things like Sulphonates & Phenates but these are piddly in comparison to what you get from Zinc.
A lot of folks misunderstand the logic for putting over-based metallic detergents in oil (the stuff that largely gives an oil its TBN & the bulk of its Ash). It has almost nothing to do with 'cleaning' or high sulphur fuels. The first 5 TBN is usually there for rust prevention as defined by the Ball Rust Test. This might get raised to about 8 TBN to neutralise the complex carboxylic acids that form when base oils oxidise as they get exposed to hot, reactive blow-by gas. Typically 8 TBN is way too much for oil in normal service but it would definitely all get used up in the severe industry oxidation tests like the Sequence IIIG.
There's no harm in buying oils with 10+ TBN but TBH, there's not a lot of benefit to be gained either. The fact is that modern base oils (Groups II/III/IV/V) are massively more resistant to oxidation than old fashioned Group Is. If they're not breaking down, then there's nothing for the detergent to neutralise, so any excess just sits in the oil, doing naff all, until it's time to throw the oil away.
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