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Vulcanizates of several fluoroelastomers, listed in Table 14.1, were exposed to a standard 5W-30 engine oil, ASTM Service Fluid 105, for up to 6 weeks at 150°C (302°F).⁵ The oil was changed weekly, but was not aerated. Retained elongation was measured after exposure for 1, 2, 3, and 6 weeks; data are shown in Fig. 14.3. The results indicate that bisphenol-cured FKM-A500 VDF/HFP copolymer, FKM-B600 VDF/HFP/TFE terpolymer, and peroxide-cured FEPM-7456 TFE/P/VDF terpolymer lost most of their original elongation over the course of the test exposure, indicating considerable additional cross-linking occurred by reaction with amine- and phenol-containing oil additives. The other fluoroelastomers showed better retention of elongation, being much less susceptible to additional crosslinking. Note that FEPM-7456 contains a high level of VDF (about 30%), while FEPM-7506 contains a relatively low VDF level (10–15%) to serve as cure site for bisphenol curing. The other FEPM types contain no VDF.

Synthetic blend oil offers the best of both worlds. It has many of the characteristics of full synthetic oil, but at a much lower price. This type of oil is a mixture of synthetic and conventional base oils, plus some additives, for extra resistance to oxidation and excellent low-temperature properties. Synthetic blends make it easy for drivers to make the switch from conventional to synthetic oil, which is why this type of oil is becoming increasingly popular among today’s savviest drivers. It’s also a great middle ground for drivers who want the added protection and performance of a synthetic oil, but might not be ready to foot the bill for a total switch to full synthetic oil.