The disadvantages of synthetic motor oils include:
• Potential stress cracking of plastic components like POM (polyoxymethylene) in the presence of PAOs (polyalphaolefins).
Polyoxymethylene[ (POM), in the USA also commonly known under DuPont's brand name Delrin, is an engineering plastic, a polymer with the chemical formula -(-O-CH2-)n-. It is often marketed and used as a metal substitute, Delrin is a lightweight, low-friction, and wear-resistant thermoplastic with good physical and processing properties and capable of operating in temperatures in excess of 90 degrees Celsius (approx 200 degrees Fahrenheit). According to the material safety data sheet from DuPont, the material has a slight odor of formaldehyde.[1]
It is also known as polyacetal, acetal resin, polytrioxane, polyformaldehyde, and paraformaldehyde; the latter term is usually restricted to the short-chained polymer. The plastic is sold under the trade names Kepital, Celcon, Hostaform and Ultraform, the last three being copolymers.
Polyalphaolefin is by far the most common major synthetic base oil used in industrial and automotive lubricants. It is a synthetic hydrocarbon (SHC) that mimics the best hydrocarbon (branched) structure found in mineral oils.