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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.

An oil seal, also known as crankshaft retainer, is a small device, but essential to ensure the proper engine operation. It plays a key role in all moving parts of an engine, acting as a physical barrier. This mechanical seal fulfils the dual purpose of sealing a rotary shaft to maintain the necessary lubrication (avoiding leaks) and preventing other foreign matter from contaminating shafts and bearings in the rotary shaft equipment.