I guess that we need to clarify first what esters and pao's are so lets start with this.
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 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.
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.
When we talk about oils which contain ester basestocks they are generally a blend of ester and pao. Only aviation oils as far as I am aware contain 100% ester hence their incredible cost but also incredible performance.
Top oils designed to be used in race applications like Silkolene Pro and Motul 300v contain a good slug of ester around 20% with the balance being pao.
To understand the types of basestock, you need to look at the API basestock classifications. I think I've posted this before but here goes again.
Basestock categories and descriptions[/b]
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All oils are comprised of basestocks and additives. Basestocks make up the majority of the finished product and represent between 75-95%.
Not all basestocks are derived from petroleum, in fact the better quality ones are synthetics made in laboratories by chemists specifically designed for the application for which they are intended.
Basestocks are classified in 5 Groups as follows:
Group I
These are derived from petroleum and are the least refined. These are used in a small amount of automotive oils where the applications are not demanding.
Group II
These are derived from petroleum and are mainly used in mineral automotive oils. Their performance is acceptable with regards to wear, thermal stability and oxidation stability but not so good at lower temperatures.
Group III
These are derived from petroleum but are the most refined of the mineral oil basestocks. They are not chemically engineered like synthetics but offer the highest level of performance of all the petroleum basestocks. They are also known as "hydrocracked" or "molecularly modified" basestocks.
They are usually labelled/marketed as synthetic or semi-synthetic oils and make up a very high percentage of the oils retailed today.
Group IV
These are polyalphaolefins known as PAO and are chemically manufactured rather than being dug out of the ground. These basestocks have excellent stability in both hot and cold temperatures and give superior protection due to their uniform molecules.
Group V
These special basestocks are also chemically engineered but are not PAO.
The main types used in automotive oils are diesters and polyolesters. Like the group IV basestocks they have uniform molecules and give superior performance and protection over petroleum basestocks. These special stocks are used in all aviation engines due to their stability and durability. Esters are also polar (electro statically attracted to metal surfaces) which has great benefits. They are usually blended with Group IV stocks rather than being used exclusively.
It is common practice for oil companies to blend different basestocks to achieve a certain specification, performance or cost. The blending of group IV and V produces lubricants with the best overall performance which cannot be matched by any of the petroleum basestock groups.
Finally, the quality of the oil you use should be selected on several criteria.
1. Cars use
2. Cost
3. Oil change periods
With regards to whether Porsche approves an oil - Not wishing to be controversial here but does this not apply to cars under warranty?
Just because an oil is not approved by Porsche, does it make it unsuitable?
The fact is that it's not to do with an oil failing Porche's tests but that it has not been tested and therefore does not appear on the list. In general, the main reason that oils are not tested is because the Oil Company does not wish to pay the high testing fees, not because the oil would not meet the required spec. It is no fluke that there are far more oils on the market that are Ford Approved than Porsche Approved, it is a far bigger market for the Oil Company, what would you do in their shoes?
If you take many high performance oils, especially race ones, they would exceed the performance of the likes of Mobil1 so why exclude using them unless of course the car is under warranty as you may give the Dealer an excuse to sidestep a problem if one occurs. Out of warranty the correct viscosity and quality for your application is the important thing.
Are esters better? Yes, from what eminent chemists have told me over the years I believe they are.
Do you need them? Application and Cost are the key.
In a track car or a car that is driven hard they are more essential than in a car that sits in the garage for 11 months a year and is never driven hard.
We're always here to help in the Oil/Fuel section, just ask...........we don't bite.
Cheers
Simon
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