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Boris Zhmud holds a PhD in Surface Chemistry and is Associate Professor in Physical Chemistry at Lund University in Sweden.

Moderator: Tech Support Mod

Boris Zhmud, BIZOL, Germany

Technically speaking, any motor oil consists of a base oil and an additive package. The American Petroleum Institute (API) categorize 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 IV base oils are full synthetic (polyalphaolefin or PAO) oils. Group V is for all other base oils not included in Groups I through IV.
We are all aware of advantages of full synthetic oils: exceptional oxidation stability, cleanliness, good lubrication performance both at temperature extremes, low evaporation losses, exceptional lubricant film strength for superior wear protection, fuel efficiency, and long service life. The problem is that, nowadays, nearly any oil you can find on your auto parts store shelf is claimed to be fully synthetic. It all started in the late 90s, after Mobil lost their lawsuit against Castrol regarding the use of term “synthetic” for Castrol’s SynTec hydrocracked oils. This has opened the door to all oil companies to label the cheaper hydrocracked oils as synthetics.
Manufacturing cost savings give a very strong temptation for calling “fully synthetic”something which isn’t really so: you pay ca 1000 USD/mt for mineral base oil, ca 1500 USD/mt for hydrocracked “synthetic” base oil of API Group III and ca 3000 USD/mt for truly synthetic polyalphaolefin (PAO) base oil of API Group IV. Prices of some specialty synthetic base stocks may reach 10,000 USD/mt.
To give you some idea regarding the percentage of “truly synthetic” oils in “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 synthetic base oils of API Group III/III+: ca 30-50% in SAE 5W 20 or 30, and even a smaller percent of PAOs. On the contrary, all BIZOL premium products are formulated exclusively from Groups III-V base oils, and hence are truly “fully synthetic”.
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Figure 1 / Typical percentage of synthetic base oil in mainstream “synthetic” motor oils (Courtesy Alain Mathivaud, Total).

Contrary to popular belief, “truly fully synthetic” motor oils are never formulated from PAO alone. And they were so, they would have failed some essential quality criteria, such as seal compatibility and dispersancy. To compensate for the deficiencies of PAO, solvency and lubricity boosters are required, which may be mineral oils (surprise, surprise), alkylated naphthalenes, 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.
It should also be remembered that many performance specifications are self-excluding and no single oil can meet all of them. For instance, an oil claiming ACEA A3/B4 cannot claim ACEA C1 at the same time. Unfortunately, it is not unusual that some careless manufacturers neglect this.
What are major advantages of fully synthetic oils. First, one should mention outstanding oxidation resistance, making it possible to extend drain interval even under harsh exploitation conditions. Since the oil price as such constitutes only a fraction of the total service cost, it makes a lot of sense to max up drain interval: you will save money by using an oil with a twice longer service interval even if the oil is twice more expensive than usual.
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Figure 2 / Oxidation resistance of typical 150N grades (6 cSt at 100C) in RBOT test (min). Higher is better.

Oxidation stability can be boosted further by using Group III and IV base oils in combination with alkylated naphthalenes. This technology is used in particular in BIzol Green Premium line of fully synthetic motor oils.
Another important advantage is the superior low-temperature pumpability of fully synthetic products. This guarantees easy motor start, effective lubrication and longer battery life in cold winters. Figure 3 gives a comparison of CCS (cold crank simulator) viscosities at -25C for typical 150N (6 cSt at 100C) grades. Starting a cold engine with a fully synthetic motor oil product, such Bizol Green Premium, consumes 5-6 less battery power, significantly extending the battery life and protecting motor against the most aggressive starting-up wear.
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Figure 3 / Viscosity of different 150N base oil grades at -25C (cP). Lower is better.

Finally, use of synthetic base oils allows one to max up lubricant film strength, resulting in superior wear protection and improved fuel economy.
The next diagram illustrates how our commitment to stay truly fully synthetic boosts the performance of our products over the mainstream level.
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FIGURE 4 / Comparison a truly fully synthetic Bizol Green Premium SAE 5W-30 ACEA C3 motor oil with the baseline category performance specifications.

Last, but not least: One very useful property of synthetic base oils are the constancy of their properties: C10 PAO 6 is always C10 PAO 6, showing very small variations in physicochemical properties across different manufacturers. However, Group I, II and to lesser extent Group III base oils may show rather large variations in the properties - depending on the crude type, refinery and season - even for the same product coming from the same refinery. This is inevitably reflected upon the quality of the finished products.