Maurice,
No, it's not what I'm saying but there are certainly more HC/MC oils out there today than real synthetics. The reasons are clear, if something can be labelled as a synthetic but costs a fraction to make then more profit for the oil companies.
All companies make a percentage of real synthetics but these tend to be a small percentage as they are costly to make.
You can pretty much guarantee that a 0w or 5w oil will be a PAO or Ester blend as generally only pure synthetics will pass the 0w or 5w tests. Pretty much all oils that are 10w, 15w and 20w etc will be either HC/MC or Mineral oils. There are some exceptions however like Silkolene's PRO range of Ester based products, Mobil 1's PAO blends, Fuchs Supersyn PAO's and Total's Quartz 9000 range of oils.
It is a mixed bag and you have to be careful, data is required which is often not available and therefore chemical analysis is the only sure route to knowing.
As for Castrol well, to quote a few products, SLX 0w-30 and RS 0w-40 are true synthetics and RS 10w-60 is not.
The key point here is, a pretty can on a shelf labelled "synthetic" probably is not and therefore you may not be getting what you're paying for.
Here is something that was written by John Rowland (Silkolene/Fuchs Chief R&D Chemist) which explains things from a chemists point of view, not a salesman.
Building a good oil
A cave may not be the best place to live, but it's ready-made and cheap. This is the estate agent's equivalent of an old style monograde oil. Or you could get Hengist Pod to fit a window and a door; this is moving up to a cheap and cheerful mineral 20w-50. But an architect-designed "machine for living in", built up brick by brick, is an allegory of a high performance synthetic oil.
It is impossible to make a good 5w-40, or even 10w-40, using only mineral oil. The base oil is so thin, it just evaporates away at the high temperatures found in a powerful engine that is being used seriously. Although there are chemical compounds in there to prevent oil breakdown by oxygen in the atmosphere (oxidation) they cannot adequately protect vulnerable mineral oil at the 130 degC plus sump temperatures found in hard worked turbocharged or re-mapped engines.
Synthetics are the answer. They are built up from simple chemical units, brick by brick so as to speak; to make an architect-designed oil with properties to suit the modern engine.
But sometimes, if you look behind the façade, there is a murky old cave at the back! This is because the marketing men have been meddling!
The Synthetic Myth
What do we mean by the word "synthetic"? Once, it meant the "brick by brick" chemical building of a designer oil, but the waters have been muddied by a court case that took place in the USA a few years ago, where the right to call heavily-modified mineral oil "synthetic", was won. This was the answer to the ad-man's dream; the chance to use that sexy word "synthetic" on the can"¦.without spending much extra on the contents! Most lower cost "synthetic" or "semi-synthetic" oils use these hydrocracked mineral oils. They do have some advantages, particularly in commercial diesel lubricants, but their value in performance engines is marginal.
TRUE synthetics are expensive (about 6 times more than top quality mineral oils). Looked at non-basically there are three broad catagories, each containing dozens of types and viscosity grades:-
PIB's (Polyisobutanes)
These are occasionally used as thickeners in motor oils and gear oils, but their main application is to suppress smoke in 2-strokes.
The two important ones are:
Esters
All jet engines are lubricated with synthetic esters, and have been for 50 years, but these expensive fluids only started to appear in petrol engine oils about 20 years ago. Thanks to their aviation origins, the types suitable for lubricants (esters also appear in perfumes; they are different!) work well from ""50 degC to 200 degC, and they have a useful extra trick.
Due to their structure, ester molecules are "polar"; they stick to metal surfaces using electrostatic forces. This means that a protective layer is there at all times, even during that crucial start-up period. This helps to protect cams, gears, piston rings and valve train components, where lubrication is "boundary" rather than "hydrodynamic", i.e. a very thin non-pressure fed film has to hold the surface apart. Even crank bearings benefit at starts, stops or when extreme shock loads upset the "hydrodynamic" film. (Are you listening, all you rally drivers and off road fanatics?)
Synthetic Hydrocarbons or POA's (Poly Alpha Olefins)
These are, in effect, very precisely made equivalents to the most desirable mineral oil molecules. As with esters, they work very well at low temperatures, and equally well when the heat is on, if protected by anti-oxidants. The difference is, they are inert, and not polar. In fact, on their own they are hopeless "boundary" lubricants, with LESS load carrying ability than a mineral oil. They depend entirely on the correct chemical enhancements.
PAO's work best in combination with esters. The esters assist load carrying, reduce friction, and cut down seal drag and wear, whilst the PAO's act as solvents for the multigrade polymers and a large assortment of special compounds that act as dispersants, detergents, anti-wear and oxidant agents, and foam suppressants. Both are very good at resisting high-temperature evaporation, and the esters in particular will never carbonise in turbo bearings even when provoked by anti-lag systems.
I'm off on holiday now for two weeks and will dig out some good stuff from our archives on my return so I'll see you all then. Happy reading!
Cheers
Simon
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