* Operating Temperature: Refrigeration oils need to remain stable and fluid at much lower temperatures than engine oils. Refrigerant systems can operate at temperatures well below freezing, while engine oils need to function in high-heat environments. Refrigeration oils typically have a much lower pour point (the temperature at which they become too viscous to flow).
* Miscibility with Refrigerant: This is perhaps the most crucial difference. Refrigeration oils must be compatible with the refrigerant used in the system. They must be miscible (able to mix) with the refrigerant, preventing separation and ensuring proper lubrication of compressor components. Engine oil is not designed for this and would likely cause serious problems in a refrigeration system.
* Chemical Stability: Refrigeration oils need to be chemically stable in the presence of refrigerants, which can be corrosive or reactive. Engine oils aren't designed for this specific interaction and might degrade quickly, leading to system failure.
* Viscosity: While both oils have viscosity grades, the range and characteristics differ significantly. Refrigeration oil viscosity needs to be maintained over a much wider temperature range, particularly on the low end.
* Additives: The additives in refrigeration oils are chosen for compatibility with refrigerants and for low-temperature performance. Engine oils contain additives designed to handle high temperatures, combustion byproducts, and wear resistance in a completely different environment.
In short, using engine oil in a refrigeration system would be disastrous. It would likely lead to compressor failure, system leaks, and potentially dangerous operating conditions. Similarly, using refrigeration oil in an engine would offer poor lubrication, lead to increased wear, and result in engine damage. They are designed for entirely separate applications and are chemically distinct.
