Short answer
A grease’s dropping point is the temperature at which, under standard laboratory heating, it becomes fluid enough for a drop to fall from the test cup. It is measured by ASTM D2265 or ISO 2176. It indicates how a thickener tolerates heat, but it is not the temperature a grease can run at in service, which is always well below the dropping point.
How the test works
A small cup with a hole in the bottom is filled with grease, fitted with a thermometer and heated in a controlled way. The temperature at which the first drop falls through the opening, adjusted by a formula that accounts for the block temperature, is the dropping point.
ASTM D2265 uses an aluminum block heater and covers a wide temperature range. The older ASTM D566 method, which used an oil bath, was withdrawn by ASTM in 2023 with users directed to D2265; ISO 2176 remains in use internationally.
Why it is not an operating limit
ASTM’s own method notes caution that dropping point does not indicate a grease’s maximum usable temperature. In service, a grease’s life at temperature depends mostly on the oxidation of its base oil, evaporation and bleed, not on the point at which the thickener lets go. Data sheets that list an operating range alongside the dropping point give a better picture.
Typical differences by thickener
Simple soap greases, such as simple lithium or calcium, generally have lower dropping points than complex-soap greases such as lithium complex, aluminum complex or calcium sulfonate complex. Some non-soap thickeners, such as organoclay (bentonite), do not melt in the usual sense and may not show a meaningful dropping point at all.
Specifications use dropping point as a screening limit. In ASTM D4950, for instance, the wheel bearing category GC calls for a higher minimum dropping point than the chassis category LB.
Dropping point in compatibility testing
When two greases are mixed, the blend’s dropping point can fall below that of either grease. The ASTM D6185 compatibility practice uses dropping point as one of its criteria, which is one reason to purge old grease when changing products rather than simply pumping new grease on top.
Frequently asked questions
Is a higher dropping point always better?
A higher dropping point shows greater thickener heat tolerance, but it does not guarantee longer life at temperature. Oxidation stability, base oil and the application matter more.
What dropping point do wheel bearings need?
ASTM D4950 sets a minimum for the GC wheel bearing category. Follow the vehicle maker’s grease specification rather than choosing on dropping point alone.
General maintenance information. Always follow your vehicle or equipment manufacturer’s requirements and the current product data. Questions? Email [email protected].