Definition
NOACK volatility (ASTM D5800 / CEC L-040) measures the evaporative loss of a lubricant when heated to 250°C for one hour under defined airflow conditions. It expresses how much of the oil (by mass %) evaporates under these conditions.
Low volatility is desirable because:
- Oil consumption is reduced — lighter fractions evaporate preferentially
- Viscosity increase is minimized — loss of light fractions raises average molecular weight
- Emission targets are met — evaporated oil contributes to hydrocarbon emissions
Typical NOACK limits:
- API SP / ILSAC GF-6: maximum 15% evaporative loss
- ACEA C (low-SAPS): maximum 13%
Base oil quality strongly affects NOACK values. Group III and Group IV (PAO) base oils have inherently lower volatility than Group I or Group II.