Synthetic Motor Oil

What is synthetic motor oil?

In the strictest sense, synthetic motor oil is made from Group 4 polyalphaolefin (PAO) base stock, with ester blended in to help various additives dissolve and also provide seal compatibility. But oil made from crude can masquerade as synthetic (more on that below) Amsoil was the first company to introduce a PAO/ester synthetic oil in 1972, followed by Mobil Corporation. But not all synthetic oil is PAO/ester.

Synthetic motor oil has several meanings

In 1990’s he American Petroleum Institute (API) introduced the Engine Oil Licensing & Certification System that divided base oils in to groups. That started a debate as to exactly how to define the words “synthetic”motor oil.

The debate began because of the API’s designation of Group I through III oils. Group 1 through III oils are refined from crude oil. Group III oils are refined using a severe refining process like catalytic cracking, hydro-isomerization and catalytic dewaxing, or by polymerization processes—which technically qualifies them as “man made,” because they’re made from “synthesized molecules.” Severe refining results in a high purity, light color, low sulfur, low unsaturated oil similar to PAO oil. In other words, Group III oil may look and act like the original “synthetic” PAO/ester oils but they’re not the same. Since they cost far less to produce, some refiners, like Castrol, Shell and BP argued that their synthesized products could be referred to as synthetic oil, since they too were “man-made.”

At the time, Amsoil and Mobil were charging a premium price for their products and felt the competition from Group III oils calling themselves “synthetic” was unfair. In 1995 the Society of Automotive Engineers (SAE) deleted the word “synthetic” as a definition in its Information Report J357 that described the physical and chemical properties of motor oil. API also deleted the word synthetic in the API 1509 document which designated Group III oils for higher refined oils and Group IV for PAO base oils.

Castrol and Mobil meet head-on in a war of definitions

Castrol introduced Castrol Syntec Motor Oil which contained 70-80% PAO and 7% ester. However, by 1998, Castrol Syntec no longer contained PAO and ester and contained only hydro-isomerized mineral oil. (Castrol had been purchasing its Group IV PAO from Mobil until the change in 1997). Since Castrol Syntec Motor Oil no longer contained PAO, Mobil claimed that Castrol could no longer claim that its product was “synthetic” and filed a complaint with the Better Business Bureau’s National Advertising Division (BBBNAD). Mobil’s contention was that true synthetics had to be formulated from small molecules subject to a chemical reaction, not built from natural petroleum. Mobil’s expert Professor J.M. Perez, a lubrication and technology expert from Pennsylvania State University argued that the hydroisomerization does not create synthetic material because it does not create or build molecules, but merely rearranges the same molecules that were present in the original petroleum fraction.

Castol countered that in 1995, both API and SAE revised its guidelines to eliminate the definition of “synthetic” and contended that Mobil’s complaint to the BBBNAD was really designed to re-open the debate Mobil had already lost in industry organizations and because the Castrol product was threatening Mobil’s market dominance in the synthetic oil market. In addition, Castrol pointed out that Shell’s hydroisomerized basestock were being marketed as a synthetic in 37 countries.

In March, 1999, the BBBNAD ruled that Castrol did not deceive consumers by claiming its Castrol Syntec Motor Oil was a synthetic oil, despite the fact that it no longer contained PAO and esters because both the SAE and API deleted their definitions of the word synthetic.

What’s the difference today between Group III and Group IV motor oil?

Since Amsoil’s and Mobil’s Mobil 1 product were the original PAO/ester Group IV products, they’ve gained a reputation as the only “true” synthetic motor oils. However, as we’ve seen with the Castrol Syntec experience, where Castrol changed from 80 to 90% PAO and 7% ester to 0% PAO, oil companies can change their product formulation at any time. Plus, they can market a PAO product in one country as a synthetic, yet supply Group III products in other countries while still calling them synthetic.

So who makes a real Group IV synthetic?

You shouldn’t assume. Group IV oils cost more to manufacture, yet, the cost difference between Amsoil and Mobil 1 products and competitors “synthetic” products has narrowed significantly. Can you assume that Amsoil and Mobil 1 or any other manufacturer like Royal Purple or Red Line are still 100% PAO/ester? Not unless the company specifically states so in their sales literature or technical information.  Think about this; if a company is really selling a PAO/ester product, they’d be proud of it and they’s scream it from the roof tops. And, since PAO/ester oils are more costly to make, you should expect to see a higher price. If it doesn’t say PAO or ester, it ain’t

More information on synthetic motor oil

Explore myths about synthetic oil here
What are the real world differences between conventional and synthetic oil. See this post
What are the oil change intervals for synthetic oil? See this post
Can you really go longer between oil changes if you switch to synthetic oil? See this post

©, 2019 Rick Muscoplat