Motor oil has to do more than lubricate engine parts. It also needs to remain stable when an engine is working hard in high temperatures.
Long highway trips, heavy towing, stop-and-go traffic, hot summer weather, turbochargers and many modern engine designs can expose motor oil to significant heat. Under enough heat, some of the lighter components in an oil can evaporate. This is called volatility.
When those lighter components are lost, an engine may use more oil between oil changes. The oil left behind can also become thicker, which may affect how easily it circulates and change the balance of the original oil formulation.
How the NOACK Test Works
The NOACK Volatility Test is a widely used laboratory method for measuring how much motor oil evaporates under controlled high-temperature conditions.
In the ASTM D5800 test, an oil sample is weighed, heated to 250°C (482°F) for one hour, and exposed to a controlled flow of air. The sample is then weighed again. The difference is reported as the percentage of the oil’s original weight lost through evaporation.
For example, if a 100-gram oil sample loses 10 grams during the test, its NOACK volatility result is 10%.
In simple terms, a lower NOACK result means less of the oil evaporated during the test.
Finding NOACK Information
Some motor-oil manufacturers publish actual NOACK volatility results in technical data sheets for individual products and viscosity grades. Others may publish only the specification an oil meets, or may not list a NOACK result at all.
When it is available, a published NOACK value gives you one more measurable property to consider when comparing oils. Compare results only between oils with the same viscosity grade and intended application, and make sure you are using current technical data.
A missing published NOACK number does not mean an oil failed the test. It only means the value was not listed in the documentation being reviewed.
Why Lower Volatility Matters
Oil volatility is only one measure of motor-oil performance, but it can be important in engines that operate under high heat or load.
Higher volatility can contribute to:
- Increased oil consumption between oil changes
- Thickening of the remaining oil as lighter components evaporate
- Additional oil vapor entering the engine’s crankcase-ventilation system
- Increased potential for deposits in areas affected by oil vapor
- Changes to the oil’s original balance of lighter and heavier components
Modern turbocharged, direct-injected and heavily loaded engines can place more demand on a motor oil than many older engine designs. Choosing an oil that meets the manufacturer’s specifications—and that is designed to perform in the conditions the vehicle sees—can help support long-term engine protection.
Industry Testing Standards
The NOACK test was originally developed and used in Europe and has become a common way for oil manufacturers and industry organizations to evaluate volatility.
Current passenger-car motor-oil specifications include limits for NOACK volatility. The exact limit depends on the industry category or vehicle-manufacturer specification, so always check the current requirements for the vehicle and viscosity grade. For example, API SP and ILSAC GF-6 limited NOACK volatility to a maximum of 15% weight loss, while GM dexos1 Gen 2 specified a more stringent maximum of 13% weight loss.
These limits are not a complete measure of oil quality. An oil must also meet the correct viscosity grade, industry classification and any vehicle-manufacturer requirements for the specific engine.
AMSOIL and NOACK Testing
AMSOIL reports that it was the first oil manufacturer in the United States to use the NOACK Volatility Test as a performance measurement in 1985, before the test became a more routine industry benchmark.
Today, NOACK volatility remains one of many measurements used to evaluate how well a motor oil can resist heat-related evaporation and help maintain performance over an oil-change interval.
Choosing the Right Oil
Start with the vehicle owner’s manual. Use the required viscosity grade and specifications listed by the manufacturer, then consider how the vehicle is actually used.
A commuter vehicle that sees short trips has different demands than a turbocharged truck that tows, a performance car driven hard in summer heat, or a work vehicle that spends long hours idling and hauling loads.
NOACK volatility is one useful part of the picture, but it should be considered alongside the full set of requirements for the engine and application.
Originally published September 2026. Technical information, product formulations, industry specifications, approvals and vehicle-manufacturer requirements can change. This article should be reviewed and updated as needed. Always verify current owner’s-manual requirements and the applicable product data bulletin.
