From Motul Ken:
In the USA there are a few different types of synthetic base stocks used in engine oils. We will touch on a few in this tech paper.
The word Synthetic is confusing; it describes a process, not a material. For example, White sand is synthesized into glass, but glass is never called "synthetic sand". Most people think that ALL Synthetic oils are made of the same base, THIS IS WRONG! For most of the USA, there are mainly THREE types of synthetic oils (or as we like to say, synthetics are DESIGNER oils).
The first type is a GROUP 3. This is a Petroleum oil that is refined to deliver a VERY good base oil. The process and end product is the least expensive of the 3 types of synthetics. Actually this type of product was considered a Petroleum oil until a recent legal battle was lost. The molecules are not as consistent in their size as in a PAO or ESTER (mentioned below) but are better than a Group 1 and 2 petroleum oil. The advantages of the G3 are a cleaner base, a higher Viscosity index (ability to flow) and better all around performance.
The second type is a (Group 4) PAO, short for POLY-ALPHA-OLEFINE -or easier to understand, it is SYNTHESIZED PETROLEUM oil. It is refined in a special process, or in simple words "synthesized". It still starts out by being pumped out of the ground (petroleum). PAO's are better than regular petroleum and G3 oils for handling heat, oxidation, low temperature startups and higher film strength. Drawback, PAO, G3, and PETROLEUM are dynamic types of oil, you have to build up oil pressure and have rotation before a film is produced. Better said, you have to HYDROPLANE the engine parts like you hydroplane a car in the rain, to create a film! (Or in the case of water-skiing, you have to build speed for the skier to get up and plane on the water) PAO's are not as expensive as esters because they are made from crude oil and produced in large quantities.
The other main type of synthetics are, SYNTHETIC ESTERS. GROUP 5 (Diester, POLYMER ESTER, Polyolesters, polyesters and COMPLEX) MotulŪ uses esters in many of its products. ESTERS ARE MOSTLY MADE OF VEGETABLES, minerals and animal fatty acids. (Motul'sŪ esters contain a lot of nut and veggie derivatives) Esters are much more expensive because the ingredients all have to be collected from natural RENEWABLE resources and synthesized (a very expensive process) in smaller quantities. Esters have all the advantages of a PAO but more of them. ESTERS CAN HANDLE HEAT BETTER THAN PAO's AND WHEN BURNED, ESTERS LEAVE FAR LESS (COKING) DEPOSITS. ESTERS ARE STATIC types of OILS and ARE ATTRACTED TO METAL PARTS WITH AN ELECTRO-CHEMICAL BOND. THIS MEANS NO MORE METAL TO METAL START UPS, This also means that a film is THERE BEFORE The Oil Pressure Light Goes Out preventing Premature Ware Of High-Stressed Parts Like Cam Lobes. The Film created is up to 5 times stronger then petroleum oil.. THE NUMBER 1 REASON TO RUN AN ESTER SYNTHETIC OIL is BOND. The Electrochemical bond is made because the ESTER MOLECULE IS POLAR! Sort of like a refrigerator magnet! It is attracted to metal and it sticks.
THE PAO MOLECULES ARE NEUTRAL and act like a piece of plastic placed on the Frig. They just fall off. FYI, all commercial jet planes use an ester synthetic of some type and not a PAO! You need to run an ester of some sort for maximum protection!
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