What is a true “Fully Synthetic” oil?

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What is a true “Fully Synthetic” oil?

Dr. Boris Zhmud, Head of Research and Development, BIZOL Lubricants, www.bizol.us

All motor oils consist of a base oil and an additive package. The American Petroleum Institute (API) categorizes all base oils into five groups: Group I to Group V. The first three groups, I, II, and III, originate from petroleum crude oil. Of those, Group I is produced by solvent refining, while Group II and III are produced by hydrocracking and catalytic dewaxing. Group III is vastly superior to Groups I and II as automotive applications are concerned, closing the gap with polyalphaolefins (PAO) which constitutes the next group, Group IV. Group IV base oils are truly synthetic oils made by polymerizing linear C8-C14 alpha-olefins such as 1‑decene. Group V is for all other base oils not included in Groups I through IV.

Top-tier crankcase lubricants that meet today’s toughest performance requirements are formulated from Group III, IV and V, though a higher API Group number does not automatically mean an upgrade in all base oil properties. For instance, some members of the API Group V are not suitable for use in crankcase lubricants at all.

With so many base oil groups, why do customers only see them described as “Mineral” or “Synthetic”?  It all started in the late 90s, after Mobil lost their lawsuit against Castrol regarding the use of the term “synthetic” for Castrol’s SynTec hydrocracked oils. This opened the door for all oil companies to label hydrocracked oils as synthetics. There are different rules in Germany where legal requirements mean that Synthetic really is Synthetic or PAO based, while Group II and III based products are called “HC Synthetic”. In the USA, to the contrary, Group II and III oils are also called Synthetic, undistinguishable from PAO.


Synthetic Graph

Figure 1 / typical percentage of synthetic base oil in mainstream “synthetic” motor oils

To give you an idea regarding the percentage of “truly synthetic” oils compared to the “claimed-to-be synthetic” motor oil products, please take a look at Fig. 1. As you can see, the majority of mainstream motor oils, albeit called synthetic, use only a relatively small fraction of high-end HC synthetic base oils of API Group III: ca 30-50% in SAE 5W 20 or 30, and even a smaller fraction of PAOs.

True Synthetic Oils are beautiful oils, have outstanding oxidation stability, cleanliness, good lubrication performance at both temperature extremes, low evaporation losses, exceptional lubricant film strength and long service life.

Oxidation resistance makes it possible to extend drain intervals even under harsh exploitation conditions. Since oil price represents only a fraction of the total service cost, it makes sense to max up drain intervals. Meaning that even with a more expensive oil change, the customer still wins.

Another important advantage is the superior low-temperature pump ability of true fully synthetic products. This guarantees easy motor start, effective lubrication and longer battery life in cold winters, protecting the motor against the most aggressive start-up wear.

Finally, the use of synthetic base oils allows one to max up lubricant film strength, resulting in superior wear protection and improved fuel economy.

But is that what is actually being sold to you? Contrary to popular belief, “true fully synthetic” motor oils are never formulated from PAO alone and always contain solvency and lubricity boosters, such as alkylated naphthalene’s, esters, and oil-soluble polyalkylene glycols. Choice of base oil type affects requirements to the additive package, so a great deal of experience is required to develop balanced formulations.

All these things mean that you may have a special oil but it is the additives and the formulator skills that make it an exceptional oil.  If you are offered a synthetic oil that is so cheap that it seems unbelievable, then it probably is.

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