Here's some info:
SYNTHETICS IN THE POWERSPORT INDUSTRY: ESTERS vs. PAO
“Base stocks” are what constitutes 75 to 80% of a finished engine oil.
In 1999, the generally accepted rules for labeling an engine oil “synthetic” blew in pieces. A major marketer
forced a court ruling allowing oils that are using “Group III – hydrocracked” base stocks to be labeled
“synthetic”. Previously, only engine oils using the following base stocks could be labeled “synthetic”:
• Group IV: PAO or Poly-Alpha-Olefine, derived from the Ethylene chemistry
• Group V, catch-all category for non-PAO synthetic. Esters are a Group V base stock.
For some high-performance applications in the Powersports industry, these cheaper Group III-synthetics
were not good enough, and to differentiate their products, many Powersports marketers started to specify
that their own synthetics were either “Ester” or “PAO”.
What is the difference between Ester and PAO applied to a 4-stroke Powersports engine oil ?
First, a few facts:
- Esters have a property that makes them prone to marketing abuse: small quantities are easily
detected in inexpensive lab testing. For example, 3% of Ester will have virtually no useful effect in a lubricant,
but a laboratory still will conclude “contains esters”, therefore “contains synthetics”. This makes it tempting for
companies to promote Ester as “the perfect elixir”, then put 3% in all their products even if it provides no
benefit for the engine.
- The Total group, maker of ELF lubricants, is the 4th largest oil company in the world and
manufactures base stocks. Total extracts crude oil, operates many refineries, operates chemical plants, and
employs 10,000 people in the US Chemical industry alone. In short, the Total group engineers and
manufactures lubricants from A to Z.
- Most specialty brands of oil in the Powersports industry are from companies that do not manufacture
any base stock, be it mineral, hydrocracked, ester or PAO. The staff of these companies is often mostly
dedicated to marketing and sales. Most of the technical development is sub-contracted to Chemical groups
such as Total, from which they purchase their base stocks.
Now, about the respective merits of Esters and PAO for motorcycle oils, let’s first have a look at their pros
and cons from a chemist’s perspective:
Qualities found in both PAO and Esters (versus Hydrocracked and Mineral base oils):
• High Viscosity Index (oil does not “melt” at high temperature),
• Very low pour point (you can start in minus degree weather)
Now the differences:
PAO Ester
Pros
- Low polarity: good foaming and
air entraining properties
- High temperature stability
- High polarity (=good lubricity)
- Straight chain molecules are biodegradable
(true of a limited number of esters)
Cons
- Low polarity (lower lubricity)
- tendency to retract and harden
the seals
- Poor hydrolytic stability (reacts to water)
- Incompatible with acrylate seals, risk of
incompatibility with nitrile and VAMAC
(depends on the type of ester)
Polarity causes the ester molecules to be attracted to positively charged metal surfaces. As a result, the
molecules tend to line up on the metal surface creating a film which requires additional energy (load) to
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penetrate. The result is a stronger film which translates into higher lubricity and lower energy consumption in
lubricant applications.
On the other hand, PAO’s low polarity means that they have better foaming and air entraining properties.
Foam and air entrainment occurs when the engine is going at very high speed (which is often the case with a
motorcycle). Foam and any bubbles formation in the lubricant is detrimental to the engine.
So we can deduct the choices that the formulator has when he makes a 100% synthetic lubricant:
1 100% ester: very unstable, incompatible for most seals. 100% ester lubricants will have to be drained
from the engine every few hours. Reserved for applications when their polarity is so necessary than their
inconvenience will be dealt with. For two-stroke applications, where the engine oil is mixed with the gas and
must burn, the instability of esters is a good thing. It is not the case for four-stroke applications.
2 Mix PAO-Ester, with balanced proportions: probably the best combination for Car racing engines.
Three drawbacks for motorcycles:
a. Motorcycles with a wet-clutch: Esters’ polarity will act on the clutch much like Friction
Modifiers do. They’ll make the clutch slip. A lubricant with strong Ester content is unlikely to pass the
Japanese JASO MA test to prevent clutch slippage.
b. Motorcycle 4-stroke oils are often used off-road where the environment is not as controlled as
on the race track: you may have to cross a river at low speed, and your Ester oil may not like the water…
c. The attraction of the oil to the metal is no longer needed at high speed, when hydrodynamic
lubrication is protecting the metal (the equivalent of “aquaplaning” in your engine). On the contrary, the
attraction of the Ester molecule to the metal will slow that “hydrodynamic” phenomenon and may cost
horsepower. At high speed, the resistance to high temperature and to foaming that PAO provides is more
important than the low-speed lubricity provided by some esters.
3 100% PAO, with or without a few drops of Ester. Esters are sometimes used in small quantities as a
seal-softening agent, to counter seal-hardening. They can also be used as a “marketing boosting” additive
(see earlier note on its detection by lab test), in which case, the label proudly claims “Ester synthetic” but also
“JASO MA”.
Overall PAO will have a better high temperature stability and oxidation resistance than most esters. This is
most important for motorcycle-specific lubricants since motorcycle engines will be working under higher
revolutions and overall at higher temperatures than car engines.
ELF Moto 4XT 10W50 and ELF Sport Campione 10W60 are 100% PAO, with the proper additivation to
prevent seal hardening, and performance on the clutch that allows to pass the JASO MA test.
On the other hand, ELF chose 100% Ester base stocks for its 100% synthetic two-stroke oils.
In the ELF 4XT 10W50 and ELF Campione 10W60, Total engineers put all the experience of the group to
make these the best 4-stroke motorcycle oils on the market by their combination of:
- viscosity range: notice the large viscosity range 10W50 and 10W60 for a 100% PAO synthetic with
extreme temperature resistance. Most European dirt bikes now,
- Clutch compatibility (the only 100% PAO oil to meet JASO MA with a 10W50 viscosity !!)
- Capacity to yield horsepower: no metal attraction will slow the motion of parts.
The ELF Moto technical team.
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