Year of publication: 2000


The combustion of sulfur-containing fuel produces sulfur oxides (SOx) in the engine, which are usually almost completely emitted via the exhaust tract. However, small amounts can enter the crankcase as "blow-by" gases past the piston and thus also into the engine oil.

In conjunction with condensate (e.g. from the combustion air), sulfurous acids are formed. These acids are not very stable. When they decompose, salt components remain in the oil as sulfides, which are detected by IR spectroscopy.

The development of sulfides is favored by a higher sulfur content in the oil, the degradation of oil additives, possibly poorer combustion or too low an operating temperature (overcooling). Increased sulfation thickens the oil and increases non-ferrous metal corrosion ("consumption of BN"), especially in the case of bearing metals. Sulfation is another indicator of oil aging, along with oxidation and nitration.

Since the introduction of desulfurized fuels, sulfation has played a rather less important role.