The high temperature grease market keeps expanding because equipment keeps running hotter. I have spent 25 years as a tribologist, and the most common question I hear is not which grease has the highest dropping point. It is why a grease that looks perfect on paper fails three weeks into the summer production push. In the lab we call this thermal degradation — on your shop floor, it means unplanned downtime. That market now offers more options than ever, but without a clear selection method, more options simply means more confusion.
What We Mean by High Temperature
Conventional mineral oil greases typically cap out around 120°C continuous operation. A high temperature grease is generally formulated for continuous service above that range, using synthetic base oils such as esters, polyalphaolefins, or perfluoropolyethers. By the relevant standards — ASTM D3336 for high-temperature bearing life and ASTM D2265 for dropping point — the label "high temperature" is not just marketing. It means the grease has been tested at elevated temperatures and retained its structure.
For example, a lithium complex grease with a dropping point near 260°C may still fail at 150°C because the base oil oxidizes. The dropping point tells you when the thickener stops holding oil. It does not tell you when the oil itself starts breaking down. That distinction drives every purchasing decision in the high temperature grease market.
The Three Failure Modes You Need to Know
Three failure modes cause most high-temperature grease problems: oxidation, oil separation, and carbonization. These three failure modes are easy to miss if you only look at the temperature rating. Understanding them is the first step toward a reliable high-temperature grease program.
Oxidation happens when heat accelerates chemical reactions between the base oil and oxygen. The grease darkens, hardens, and forms varnish that blocks small clearances. Oil separation, or bleeding, occurs when the thickener cannot hold the oil at elevated temperatures. You see a puddle of oil under the bearing and a stiff cake on the raceway. Carbonization is the final stage of severe overheating, where the grease turns into a hard, brittle residue that acts like sand in the rolling elements.
If you are reading a datasheet for a product labeled high temperature grease and it lists only a dropping point, you are missing the other two failure modes. Look for oxidation stability data, such as ASTM D942 or the pressure-oxidation test, and for oil separation numbers from ASTM D6184.
Base Oil and Thickener Families That Define the Market
The high temperature grease market splits into three practical product families.
Synthetic hydrocarbon greases — usually PAO or ester-based — are the workhorses. They handle continuous temperatures from 150°C to 180°C, have good compatibility with mineral greases, and cost far less than the next tier up.
Perfluoropolyether greases, often sold under brand names like Krytox or DuPont, are the top shelf. PFPE greases are chemically inert, do not burn in pure oxygen service, and can run at 250°C or higher. That performance comes at a price — often $100 or more per pound — so they are reserved for kiln bearings, vacuum pumps, and oxygen service.
Silicone greases fill a narrow niche. They handle very low and very high temperatures, but they do not lubricate steel-on-steel as well as hydrocarbon greases, and they are not compatible with most other thickeners. In the high temperature grease market, silicone is a specialist, not a generalist.
How to Choose a Grease That Beats the Spec Sheet
Start with the bearing manufacturer's requirements, not the grease supplier's marketing. Check the bearing operating temperature range, then derate by 15% to 25% for hotspots and oil starvation at high speed.
Next, select the NLGI consistency grade. For most high-temperature bearings, NLGI 2 is the default. If the application has slow rotations and high load, NLGI 1 may be needed to ensure the grease flows into the contact zone. Never assume a stiffer grease lasts longer — it can channel and leave the rolling elements dry.
Then look at the speed factor, expressed as DN value (bearing bore diameter in millimeters times shaft speed in rpm). Above about 500,000 DN, a simple high-temperature grease may not have enough base oil viscosity to form a full film. In the lab we call this elastohydrodynamic starvation — on your shop floor, it means accelerated fatigue spalling.
Application Note: Conveyor Bearings in a Cement Plant
Application Note: I was called into a cement plant last summer where conveyor bearings were failing every two months. The existing grease met the manufacturer's temperature rating, but the actual bearing housing was running 20°C hotter than the datasheet assumed. We switched to a PAO-based high temperature grease with a higher base oil viscosity, and the bearings made it through a full season. The fix was not a more expensive grease — it was matching the grease's base oil viscosity to the actual bearing temperature.
That is the lesson. The high temperature grease market has grown because plants are pushing equipment harder. But the winning move is not grabbing the most expensive tube off the shelf. It is understanding the three failure modes, checking the relevant standards, and confirming the base oil can handle the real operating temperature.
When you are ready to review your current grease program, reach out through the contact form on this site. I can help you translate a bearing datasheet into a supplier-neutral specification — the way any good tribologist should.
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