Sulfated ash...what is it, and how much is too much?

[Sonofsonof]

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.

 

[TiGeo]

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.

I do UOAs all the time and rarely over my OCIs see a loss.of more than 5 TBN using VW502 oils.

 

[Sonofsonof]

I do UOAs all the time and rarely over my OCIs see a loss.of more than 5 TBN using VW502 oils.

Yep. That sounds like par for the course.

 

[DrDanger]

I do like knowing I have TBN to spare, when I have to gas up in the boonies at a station that looks less than ideal.
The russian oil forum gurus seem to think SAPS would be turning to abrasive particles with time/oxidation.
I have not seen the exact process that would come to be.
Also SAPS should be the biggest contributor to intake valve deposits. That makes sense as do the LSPI concerns for turbo DI engines.
I think, however, the biggest deterrent to using a high SAPS oil would be the competition between the AW/EP and
anti-corrosion/detergent additives for the same engine parts/surfaces. That surely gets worse if the oil has esters?
Any thoughts on maximum/best additive concentrations for everyday oils with a long drain interval.