In the NOACK test the oil is heated to 150 C (302 F) for one hour. The lighter oil fractions will vaporize leading eventually to oil consumption, oil thickening and a loss of performance. The test reports results in the percentage, by weight, lost due to "volatilization."
For example, before July 1, 2001, 5W-30 motor oil in the United States could lose up to 22 percent of its weight and still be regarded as "passable." Now, with GF-4, the maximum NOACK volatility for API licensing is 15 percent. European standards limit high quality oils to a maximum of 13 percent loss.