Nitration is an indicator of advanced oil aging, sealing problems and problematic operating points in internal combustion engines. The oil is contaminated with nitrogen compounds (NOx). These are produced during the combustion of fuels by oxidation of the nitrogen contained in the combustion air. This process is promoted by excess oxygen or particularly high combustion temperatures.

By far the largest proportion of NOx enters the exhaust gas aftertreatment system via the exhaust valves or, in the case of older engines, is released into the atmosphere. Small amounts enter the crankcase as blow-by gas and thus also the engine oil. These nitrogen compounds lead to changes in the base oil of the engine oil used. This change, known as nitration, is measured in the infrared spectrum according to DIN 51453. High nitration of the lubricant is mainly caused by an incorrect fuel-air mixture, inaccurately adjusted ignition, high loads or poor compression or lack of sealing between the piston and cylinder wall. Since the seal between the piston and cylinder is never perfect, even very long oil service life can lead to increased nitration even though there is no actual problem.

Increased sludge formation is often the result and varnish-like deposits may already be found on the piston rings or on the piston crown. If necessary, check the motor settings and the operating temperatures.