Top causes of grease thickening in industrial lubrication systems—and how to stop them
Key takeaways
- Cross-contamination can cause grease thickening, restricting flow and accelerating equipment failure.
- Incompatibility between base oils—not chemical reactions—is the primary cause of grease performance issues.
- PFPE/PTFE and silicone greases thicken when exposed to hydrocarbon oils, risking flow loss and downtime.
- Field testing and strict lubrication practices help identify and prevent grease compatibility failures.
Cross-contamination is a fact of life in industrial lubrication, but it brings with it a poorly understood and costly problem: certain greases, especially PFPE/PTFE and silicone-based types, thicken dramatically when exposed to hydraulic oils, gear oils, or incompatible greases. This thickening impairs flowability, clogs lubrication paths, and accelerates failure. Understanding the mechanisms behind this phenomenon helps prevent downtime and protects critical assets.
Understanding grease formulation: Base oils, thickeners, and additive interactions
Greases are engineered systems consisting of three primary components: base oil, thickener, and additives:
- The base oil, be it mineral, synthetic hydrocarbon, ester, PFPE, silicone, or halocarbon, provides lubrication.
- The thickener – lithium complex, calcium sulfonate, polyurea, PTFE, barium complex, or aluminum complex gives structure and consistency.
- Additives enhance performance with EP, anti-wear, oxidation inhibitors, and tackifiers.
When grease thickens after contamination, the cause is rarely chemical reaction. The real culprit is physical incompatibility between the grease’s base oil and the contaminant, whether hydraulic fluid, gear oil, or another grease system. The following are some examples of commonly used greases and their reactions with contaminants.
PFPE/PTFE-based greases and hydrocarbon contamination. PFPE/PTFE greases are widely used in vacuum and high-temperature applications because PTFE is chemically inert and PFPE base oils have excellent thermal stability. However, PFPE oils are immiscible with hydrocarbon-based fluids like hydraulic or gear oils. When contamination occurs, mutual insolubility displaces PFPE oil from the PTFE thickener matrix. The displaced PFPE oil migrates away, leaving a concentrated PTFE structure with less oil, resulting in dramatic thickening. Additionally, hydrocarbon contamination destabilizes PTFE particle dispersion, causing clumping and stiffness. The grease becomes too thick to flow through lubrication lines, leading to friction, heat generation, and early failure.
Some halocarbon-based PFPE/PTFE greases are engineered to overcome typical incompatibility with hydrocarbons. These formulations remain chemically inert and nonflammable while maintaining compatibility with petroleum oils. They retain flowability in contaminated environments and tolerate temperatures up to 288°C and vacuum conditions. Field validation remains essential.
Silicone-based greases and petroleum contamination. Silicone-based greases experience similar problems. Silicone oils are highly immiscible with petroleum oils. When contaminated, the grease stiffens, seals swell, and lubrication films break down, compromising protection and accelerating wear.