Oil – A Slippery Subject
It is known as the “lifeblood” of your engine and is one of the most hotly and often
debated subjects in the car community and on car forums, the RX8 Owners Club forum
testifies to this fact. So, that being said, we should start at the beginning and remind
ourselves what the function of an engine oil is.
Lubrication
Motor oil must lubricate engine components so that they will easily pass by one another
without a significant loss of power due to friction. At start-up, this is especially true. As an
engine sits, oil will run down into the sump. When the engine is started, the oil must be
quickly pumped throughout the engine to provide sufficient cranking speed for the
engine to turn over. Once running, engine oil must create a film between moving parts to
make them "slippery" which increases power, performance and efficiency.
Protection
Oil must keep engine components from coming in contact with each other and provides
vital protection against wear. Engine oils also protect against corrosion of engine
components. Oxidation of the oil and contamination through condensation and
combustion by-products all cause acids within an engine oil. If these acids are allowed to
come into contact with engine components, corrosion occurs causing premature
component failure. Engine oils are designed to combat these acids.
Cleaning
If an engine doesn’t remain clean, it will not remain efficient. Deposits within an engine
reduce fuel efficiency and rob your engine of performance. If contaminants within an oil
are left "unguarded" it will cause wear within the engine. Filtration plays a big role in this
area, the oil also has to play it's part by keeping deposits from forming within the engine
and holding contaminants in suspension until they can be removed by the oil filter.
Cooling
Engine oil is responsible for a large percentage of the cooling that takes place within
your engine. The radiator is only responsible for cooling the upper portion of your
engine. The rest of the critical engine components are cooled mainly by the motor oil
within your engine. Heat is generated within an engine from the combustion process and
the friction caused by the motion of engine components. As oil passes through the
system it is directed onto these hot surfaces in order to carry the heat away to the sump.
So, that’s what the oil is designed to do but what is oil made of and why are some oils
better than others at performing these functions.
Contrary to popular belief and a healthy pinch of myth, all oils are not petroleum based
or derived. Oil technology has moved on like everything in life as the chemists strive to
create the perfect lubricants.
There are two main components that all engine oils are made of and they are basestocks
and additives. The basestocks normally make up between 70 and 95%. Additive chemicals
are then added to enhance the positive qualities of the basestocks and to overcome any
negative qualities present.
There are two main types of basestocks used, petroleum and synthetic. Petroleum
basestocks are a purified form of crude oil and have been used as automotive lubricants
since motor oils were first developed. Synthetic basestocks, on the other hand, are
chemically engineered in a laboratory specifically for the purpose of lubrication. They are
engineered from pure compounds that contain no contaminants which must be removed via
purification. Synthetic basestocks have been around for many years but have only been
used in the automotive market for the last 30 years.
The main types of oil basestocks commercially available in the market today apart from
the traditional mineral oils are as follows:
Hydrocracked (also referred to as Molecularly Converted Mineral Oils)
These are so pure and refined, they can now be called synthetics. They are not made
from true synthetic basestocks (as previously mentioned) but have so little in common
with traditional petroleum basestocks, that it doesn’t make sense classify them as
petroleum oils. Petroleum basestocks can be put through a super-extreme refining
process called “hydrocracking”. It is completely legal for lubricants manufacturers to
label these oils as "synthetic". These are extremely high performance petroleum
basestocks, will not perform to the same level as true synthetic basestocks like PAO
(poly alfa olefins) or Esters.
Hydrocracking 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 Mineral oils.
Types of Synthetic basestocks.
There are only three synthetic basestocks that are seen commonly in automotive
applications:
Poly alpha olefins (PAO's)
These are the most common synthetic basestocks. Many synthetics on the market use
PAO basestocks exclusively. Also known as synthesized hydrocarbons, they contain
absolutely no wax, metals, sulfur or phosphorous. They have extremely low pour points
and are very thermally stable. One drawback to using PAO's is that they are not as
oxidatively stable as other synthetics unless properly additised.
Diesters
These synthetic basestocks offer many of the same benefits of PAO's but are more
varied in structure. Their performance characteristics vary more than PAO's. When
chosen carefully, diesters provide better pour points and thermal stability than PAO's
and are a little more oxidatively stable. 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, without the aid of detergency additives.
They are also surface-active (electrostatically attracted to metal surfaces),
Polyolesters
These synthetic basestocks are similar to diesters, but slightly more complex. They have
a greater range of pour points than diesters, but some polyolester basestocks will
outperform diesters. They are also surface-active.
Other synthetic basestocks exist but are not nearly as widely used in automotive type
applications. Premium quality synthetics are normally a blend of more than one type of
PAO and/or PAO basestocks with diester and/or polyolester in order to create a
basestock which combines all of the benefits of these 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. So, You get what you pay for. Or do you?
The Synthetic Myth.
There are many oils on the shelves today labeled as “synthetic” but in the true sense of
the word they are not. They are the “hydrocracked” petroleum oils previously mentioned
and although generally superior to mineral oils they are not of the same quality as true
“made in the laboratory” synthetics.
So, why are these highly refined mineral oils called “synthetic”? It was all decided in a
legal battle that took place in the USA about ten years ago. Sound reasons (including
evidence from a Nobel Prize winning chemist) were disregarded and the final ruling was
that certain mineral bases that had undergone extra chemical treatments could be called
“synthetic”.
Needless to say, the marketing executives could not believe their luck! They realised
that this meant, and still does, that the critical buzz-word “synthetic” could be printed on
a can of cheap oil provided that the contents included a few percent of “hydrocracked”
mineral oil, at a cost of quite literally a few pence.
The chemistry of “synthetics” is complex and so is the politics. The economics are very
simple. If you like the look of a smart well-marketed can with “synthetic” printed on it, fair
enough, it will not cost you a lot; and now you know why this is the case.
Synthetics and the RX8.
How many times have we heard it “do not use synthetic oil in the rotary engine?”
Too many and there will be many more but, it’s a pretty meaningless statement unless
we as rotory engined car owners and the person making the statement fully understand
the meaning of the word “synthetic”.
As I have stated before, most oils on the shelves today do not contain true synthetics,
they are merely highly refined mineral oils and as such are just a high performance
mineral oil.
I have done much research into this topic since I picked up my shiny Velocity Red RX8
more than 12 months ago and I have to say with no definitive conclusion. I know of RX7
and RX8 Owners that use fully synthetic oils in their rotories with no evidence of any ill
effects to the engine, it’s not surprising as they are without doubt superior lubricants.
However, when the RX8 Owners Club asked Mazda UK about the use of Fully Synthetic
oils we received the following prompt reply.
“The Mazda RX-7 engine contained rubber parts that would be affected by synthetic oil
so dealers were told not to use it in rotary engines. We asked on Mazda RX-8 training if
this was still the case for the new Renesis engine and were told that although the rubber
parts in the engine were all now believed to be synthetic oil compatible Mazda
Corporation had not done any testing or evaluation with synthetic oil.
Mazda Corporation has developed and tested this engine using mineral oil and has
recommended its continued use in service, I would consider that straying from a proven
and tested specification is not some thing that we could endorse. Although the oil may
be a superior lubricant, there is no requirement for it in an engine with only three major
moving parts none of which are reciprocating and all of which are in near perfect
balance.”
In itself not really conclusive, the seals are compatible but it’s not been tested. So I
decided to take a trip all the way to Stoke (Belper to be precise) to talk with the Silkolene
technical boffins and the chief chemist about this reply and synthetic compatability.
Their first comment on Mazdas statement was that depending on what synthetic they are
referring to i.e. PAO (Poly Alpha Olefin), Polyolester or Diesester the seals would be
affected in different ways.
PAO's always shrink seals
Esters always swell seals
They (Silkolene) tested a mixture of PAO/Ester in the early Norton Rotary Bikes as they
were asked to formulate a "proper" synthetic for the Manufacturer and they found that
the correct formulation had the affect of no swell or shrinkage of seals.
They told me that "proper" synthetics PAO/Ester blend types are of great benefit to the
Rotary engine and the "shear stability" of these oils added to the "polar" benefits of ester
make these oils perfect for the engine.
Their reply to Mazdas comments on the engine itself were as follows:
This does not make sense, Esters have been used in the aviation industry for more then
50 years and jet engines have less moving parts in more perfect balance. Think about it!!
I also discussed the old chestnut that synthetics don’t burn as cleanly and this is totally
untrue, they in fact burn far more cleanly as they have less additives to cause deposits
such as ash and are in fact much better for your catalytic convertor.
So, my conclusion is, "true" synthetics are better for your rotary engine (although
untested) but they cost more and in a car that uses around 1 litre per thousand miles I
suspect that they are quite simply not required and costly considering that the oil is not in
the engine long enough to "shear" or "degrade" to any great extent.
So, my advice would be to use a decent, brand named 5w-30 with an API spec of SL
and ACEA spec of A1/A3 which carries the FORD spec WSS M2C913 A/B and you
really can’t go wrong. If you want to pay out for proper synthetic oils then it’s your money
and your car and although Mazda don’t endorse it the case for using them looks a pretty
convincing one and I for one am prepared to be the guinea pig. I’ll keep you posted!
Top brand Approved Oils are available through the Club at great prices.
Simon Barnard (aka Oilman)