Low SAPS or low ash
Many manufacturers of motor oils advertise their newest oils with the designation “low SAPS” or “low ash”. What does this term actually mean?
The abbreviation SAPS stands for “sulphated ash, phosphorus and sulphur”. A low-SAPS motor oil is therefore an oil with a low proportion of sulphate ash, phosphorus and sulphur. These oils are also designated “low-ash” due to their low tendency to ash formation. The requirement to use low-ash additives in the formulation of modern motor oils may sound simple, but developing this sort of motor oil is a true challenge for every lubricant producer.
Requirements for low-SAPS lubricants are relatively recent. Compliance with stricter emission standards could only be achieved by installing catalytic converters or particle filters. For proper operation, these components required new types of motor oils with a low tendency to form ash deposits and fewer additives containing sulphur and phosphorus. If too many residues remain when the motor oil is incinerated (the laboratory test is performed at 800°C), the fine pores of the diesel particle filter or the vanes of the catalytic converter quickly become plugged and their lifetime decreases drastically. Phosphorus and sulphur are highly poisonous to catalytic converters. They render the surfaces inert and impair the function of removing toxic substances from the exhaust gas in all types of catalytic converters for diesel, petrol and gas engines.
As shown by oil analyses, conventional high-performance motor oils have a high concentration of metallo-organic active substances. For a long time, the standard wisdom was that the more calcium, magnesium, boron, zinc, and (of course) phosphorous and sulphur a motor oil contained, the better was its alkali reserve (BN), and thus the better the oil. After all, the additives are what provide high wear protection and good engine cleanness. The proportion of additives has been significantly reduced due to exhaust after-treatment. This was made possible by using low-sulphur fuel and by modern oil technology and engine technology. In this way, emissions of harmful substances have been markedly reduced. However, it was necessary to develop entirely new additive packages in order to combine this with fulfilling increasingly demanding requirements for longer oil change intervals, less friction, and good wear protection.
The trend is inevitably heading toward increasing use of low-ash, low-SAPS oils. This is also reflected in the specifications of the Association des Constructeurs Européens d’Automobiles (ACEA) and the specific oils approved by vehicle manufacturers. ACEA E6 motor oils for utility vehicles are allowed to have a maximum ash content of 1.0%. Since 2004, ACEA C1 to C4 also take this into account for passenger cars. They all specify significantly reduced proportions of ash-forming substances in motor oils as a prerequisite for achieving a longer useful life of catalytic converters and particle filters.
Using low-SAPS motor oils is particularly imperative with modern vehicles. However, when selecting a suitable motor oil you should always observe the specifications or oil types approved by the engine manufacturer in the operating manual. Modern oils only work properly with the fuels specified in the EU, which are designed for modern engines with their exhaust aftertreatment systems in cooperation with low-SAPS oils.
Subsequent addition of additives is fundamentally prohibited because such additives always increase the ash content. An oil analysis can show whether a particular oil is an unadulterated low-SAPS oil.
ÖlChecker Spring 2010, page 8