Volatility is the property of the lightest fractions of the engine oil to evaporate at high temperatures, which is expressed as a percentage of loss from evaporation after heating the engine oil for one hour at 250 °C.
To determine the vaporizability, or volatility, of motor oil, the Knock method is used. If 850 grams of engine oil are left after heating 1,000 grams of engine oil at 250 °C for one hour, this means that the volatility is 15% (minus 150 grams).
According to ACEA requirements, A1/B1 class oils must not volatilize more than 15%, A3/B3, A3/B4, A5/B5, C1, C2, C3, E4, E6, E7, E9 must not exceed 13%, and C4 oils must not volatilize more than 11% or equal to 11%. If the engine oil is too volatile, it will have to be filled more often and therefore the oil consumption will be high.