Here is some more reading for those interested:
"HYDROCRACKED" (HC) or MOLECULARLY CONVERTED (MC) BASESTOCKS
There are many petroleum oils available on the
market that are so pure and refined, they can now be passed off as synthetics.
They are not made from true synthetic basestocks (at least not in the
way that synthetics have traditionally been defined), but they have
so little in common with traditional petroleum basestocks, it is really
somewhat silly to classify them as petroleum oils.
Petroleum oil basestocks can be put through a super-extreme refining process called “hydrocracking”. In some cases, as in the case of one particular name-brand "synthetic" oil, these highly refined petroleum basestocks can actually be termed and sold as "synthetic".
It is completely legal for lubricants manufacturers to label these oils as "synthetic".
These are extremely high performance petroleum basestocks, but they are not truly synthetic the way that most people understand the term and will not necessarily perform to the same level as a premium synthetic oil like PAO (poly alfa olefins) or Esters.
Hydrocracking involves changing the actual structure of many of the oil basestock molecules by breaking and fragmenting different molecular structures into far more stable ones. This results in a basestock which has far better thermal and oxidative stability as well as a better ability to maintain proper viscosity through a wide temperature range - when compared to a typical petroleum basestock.
Although contaminants are still present, and these are still petroleum basestocks, contamination is minimal and performance characteristics are high. This process also can turn a wider range of crude oil stock into well-performing petroleum lubricant basestocks.
TYPES OF SYNTHETIC BASESTOCKS
Synthetic basestocks are not all the same. There are few different chemical types that may be used as synthetic basestock fluids. There are only three that are seen commonly in automotive applications:
Polyalphaolefins (PAO's)
These are the most common synthetic basestocks used in the US and in
Europe. In fact, many synthetics on the market use PAO basestocks exclusively.
PAO's are also called synthesized hydrocarbons and contain absolutely
no wax, metals, sulfur or phosphorous. Viscosity indexes for nearly
all PAO's are around 150, and they have extremely low pour points (normally
below –40 degrees F). Although PAO's are also very thermally stable,
there are a couple of drawbacks to using PAO basestocks. One drawback
to using PAO's is that they are not as oxidatively stable as other synthetics.
But, when properly additized, oxidative stability can be achieved.
Diesters
These synthetic basestocks offer many of the same benefits of PAO's
but are more varied in structure. Therefore, their performance characteristics
vary more than PAO's do. Nevertheless, if chosen carefully, diesters
generally provide better pour points than PAO's (about -60 to -80 degrees
F) and are a little more oxidatively stable when properly additized.
Diesters also have very good inherent solvency characteristics which
means that not only do they burn cleanly, they also clean out deposits
left behind by other lubricants - even without the aid of detergency
additives.
They do have one extra benefit though, they are surface-active (electrostatically
attracted to metal surfaces), PAO’s are not “polar”,
they are “inert”.
Polyolesters
Similar to diesters, but slightly more complex. Greater range of pour
points and viscosity indexes than diesters, but some polyolester basestocks
will outperform diesters with pour points as low as -90 degrees F and
viscosity indexes as high as 160 (without VI additive improvers). They
are also “polar”.
Other synthetic basestocks exist but are not nearly as widely used as those above - especially in automotive type applications. Most synthetics on the market will use a single PAO basestock combined with an adequate additive package to provide a medium quality synthetic lubricant. However, PAO basestocks are not all the same. Their final lubricating characteristics depend on the chemical reactions used to create them.
Premium quality synthetics will blend more than one "species" of PAO and/or will blend these PAO basestocks with a certain amount of diester or polyolester in order to create a basestock which combines all of the relative benefits of these different basestocks.
This requires a great deal of experience and expertise. As a result, such basestock blending is rare within the synthetic lubricants industry and only done by very experienced companies. In addition, although such blending creates extremely high quality synthetic oils, they don't come cheap. You get what you pay for! Or do you?
If you are looking for an oil that is more viscous (sae 50) at temperatures for your Porsche, Mobil 1 15w-50 is indeed a good one but there are others that are as good or better.
Mobil 1 MS is a PAO
Silkolene PRO R 15w-50 is a PAO/Ester
Silkolene PRO S 10w-50 is a PAO/Ester
I am in a position to help you here, not only with the Mobil 1 price but you could save more on the Silkolene products and they are arguably better because they contain ester.