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In addition to preventing oil leakage, the piston oil seal also helps to reduce friction between the piston and the cylinder wall. This is important for maximizing engine efficiency and prolonging the life of the engine components. By reducing friction, the seal helps to improve fuel economy and reduce wear and tear on the engine.

Operating temperatures for engine oil seals (see Fig. 14.1¹ and cross-section of lip seal with garter spring in Fig. 14.2²) vary widely, depending on engine design and location within the engine. Typically, the rear crankshaft seal is subjected to much higher temperatures than the front seal. Oil sump temperatures vary considerably, depending on provisions for oil cooling. This allows use of hydrogenated nitrile (HNBR), silicone, or acrylic elastomers for some seals in relatively low-temperature environments (120–140°C or 250–284°F). Standard fluoroelastomers (FKM), bisphenol-cured VDF/HFP/TFE terpolymers with 68–69% fluorine content, perform well in oil service up to about 160°C (320°F). More resistant fluoroelastomers are necessary for reliable long-term performance in more severe environments.