A look at some of the differences between the API SN, SN PLUS and SP Service Categories
The API SN PLUS Service Category was introduced as a supplement to the API SN specification in 2018 to mitigate Low Speed Pre-Ignition (LSPI) events in Turbocharged Gasoline Direct Injection (TGDI) engines. Such LSPI events can cause engine knocking, decreased efficiency, and in the worst case, catastrophic failure due to cracked pistons.
As seen by the differences in the API SN and SN PLUS samples examined by PQIA, the average of the SN PLUS formulations shows lower calcium and higher magnesium levels than API SN. The same can be seen with the new API SP Service Category, and for the same reason; to protect engines from potentially severe damage due to LSPI.
Calcium and magnesium sulfonate are the most commonly used detergent additives in motor oils. Although calcium had been favored for decades, industry research has shown fewer incidents of LSPI occurred by re-balancing detergent chemistry to reduce the level of calcium and increase the level of magnesium sulfonate in the additive package. Calcium has been shown to promote LSPI, while magnesium has little impact, good or bad.
Although there are currently no minimum or maximum levels for calcium or magnesium in the specifications for the API SN PLUS or API SP Service Categories, the chart below provides a sense for the levels typically seen. As shown, the average calcium level for 30 samples of API SN PLUS motor oils examined by PQIA is 1,242 ppm, and the average for magnesium is 642 ppm. The averages of the 18 API SP samples PQIA examined to date are similar. In both cases they represent a very significant and meaningful change from the levels seen in the samples of API SN examined by PQIA.
We bring this to the attention of consumers because some of the samples labeled API SN PLUS that PQIA has reported on present calcium levels significantly higher, and magnesium levels significantly lower, than the averages we have seen for API SN PLUS. While PQIA has observed these differences , these atypical products are labeled as licensed and certified by the API.