Selecting lubricants for high ambient temperature operations

Viscosity is chosen at operating temperature, not at ambient

An oil that gives the correct film thickness at 40 degrees C may be too thin at the 80 or 90 degrees C a gearbox actually runs at in summer. The practical move is usually one ISO grade up from the temperate recommendation, confirmed against the equipment manufacturer's viscosity requirement at the real operating temperature.

Going too far the other way costs efficiency and can starve bearings on start up, so this is an adjustment, not a blanket rule.

Grease: drop point is a limit, not a rating

The drop point is the temperature at which the grease loses its structure and the oil separates. Useful operating temperature is well below it, commonly by 40 to 50 degrees C for lithium complex thickeners.

Choose the thickener for the duty. Lithium complex covers most general industrial service with a high drop point. Calcium sulphonate handles water washout and shock loading well. Polyurea suits sealed electric motor bearings and long life applications.

Regreasing intervals halve as temperature rises

As a working rule, grease life halves for every 10 to 15 degrees C rise above roughly 70 degrees C at the bearing. An interval taken straight from a manufacturer table without adjusting for local ambient is often double what the application will actually support.

Where intervals become impractically short, the answer is usually a higher specification grease or a small automatic lubricator rather than more frequent manual attention.

Storage matters more than most sites assume

Drums stored outdoors in direct sun accelerate oxidation and, if they breathe, draw in moist air overnight. Shaded, covered storage and first in first out rotation preserve more lubricant life than any change of product grade.