Oil - A slippery topic!

[oilman]

I\'m new here but not to rotary engines as I have owned an RX8 for nearly 12 months now.

I must also confess to having an interest in oil debates as it is my livelyhood and I advise many Car Clubs on the correct and best oils for their Members Cars.

I have been reading the "oil debates" here with some interest and though that it would be worth sharing what I know and my opinions with you all.

The subject of synthetic oils in the rotary engine is a much debated topic on car forums and clubs around the world but when looking at the tecnical aspects of the argument, no one has ever convinced me (or at least not until now?) that they actually cause harm to the engine or shorten its life.

To start with some basics, we need to remind ourselves what an engine oil is designed to do. It must:

Lubricate

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. Once running, engine oil must create a film between moving parts to make them "slippery" which increases power, performance and efficiency.

Protect

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.

Clean

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.

Cool

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.

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.

The most common types of Synthetic basestocks.

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.

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.

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.

Synthetics and the rotary engine.

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 nearly 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 I questioned Mazda UK about the use of Fully Synthetic oils we received the following 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 this answer is not really conclusive, the seal compatability problem seems to have been solved 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 Mazda\'s reply and synthetic compatability.

Their first comment on Mazda\'s 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 Norton and they found that the correct mix (not 50/50 I might add) had the affect of no swell or shrinkage of seals. Oils have come a long way since.

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 or at least this was their opinion.

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..................Think about it!!

Anyway, my conclusion is that "true" synthetics are better and that\'s a fact but they cost more and are not so readily available so in a car that uses around 1 litre per thousand miles was this a commercial decision as the oil\'s not in the engine long enough to "shear" or "degrade" to any great extent?

So the next question is what do I use?

I follow the handbook and use a "hydrocracked" (petroleum based highly refined mineral oil) which is in my opinion and from a chemists point of view labelled as a "synthetic" but it\'s not as the basestock is petroluem. It is a 5w-30, a 10w-30 can also be used for different ambient temperatures.

As for the RX7\'s well it\'s personal choice really and as I\'ve said before, synthetics are better but most are not true synthetics so as long as you stay clear of 100% Poly Alpha Olefin based oils (Like Mobil 1 as an example) which would give the highest levels of seal shrinkage you will be fine. An oil with a good percentage of ester basestocks will counteract this shrinkage.

There is no doubt that "hydrocracked" oils that are either Fully or semi-synthetic are fine to use because they are merely highly refined mineral oils will give you better protection than a plain old mineral oil. Silkolene actually recommend the use of their 10w-40 semi synthetic products in the RX7.

So, there it is, complicated until you know what "synthetic" really means. Hopefully this sheds some light and some food for thought on this slippery topic.

If anyone has any questions, please feel free to ask.

Cheers
Simon

[chrisBoid]

An intersting read, thanks for that

I think a lot of people use Castrol GTX 10W-40(http://www.castrol.com/castrol/productdetailmin.do?categoryId=82915280&contentId=6008816), a highly refined mineral oil that is readily available and proven, but when it comes round to buying my next tub, perhaps I\'ll evaluate what is available in the semi/synthetic range.

[wiggy]

excellent write-up

Guess what I bought for the rex before it arrived........Mobil 1 motorsport....Arghhhhh

My car looks like its had Motul used on it in the past going off the stickers and service sticker inside the door.

Looked it up and they do a nice Mineral oil that looks just the ticket

Good job I didn\'t touch it, oil is still clean and the filter looks new so I\'m guessing it was done in japan before it left?

[oilman]

In my opinion and I actually sell 6 brands of oil, it\'s hard to beat Motul and Silkolene for quality.

This is only my opinion and I do respect the views of others unless of course they use shop brands;)

Cheers
Simon

[g11ary]

Hi Oilman, no disrespect, but I wondered how long it would take for you to get on here, I noticed you\'re on every forum possible;)

Im sure you experience will be welcome.

Can I also point you in the direction of our terms and conditions for trade people.

http://www.mazdarotaryclub.com/legal/mazdarotaryclub_terms-and-conditions.htm

[iaint]

Great write-up Simon, very interesting info.

Does thi sbasically mean that stuff labelled \'semi-synthetic\' is hydrocracked or could \'fully synth\' include that too?

I use 76-racing mineral mainly because that\'s what was reccomended by the people who built my engine, not too much more pricey that castrol but much harder to get hold of!

Iain

[oilman]

Originally posted by g11ary

Can I also point you in the direction of our terms and conditions for trade people.

Thankyou and no problems. I\'m not trying to sell anything but If there is demand then of course I will become a trader willingly with the Clubs permission.

Regarding other forums.

Many Clubs (around 100) subscribe to our "Clubs Oil Scheme" and as part of it we offer an "online" advice service. You will have noticed that we usually have a dedicated thread with the Club Committee or Sight Owners permission.

I\'m not hiding the fact that we sell oils but it\'s always above board.

Cheers
Simon

[oilman]

Originally posted by iaint

Does thi sbasically mean that stuff labelled \'semi-synthetic\' is hydrocracked or could \'fully synth\' include that too?
Iain

Yes basically but it\'s a little more complicated than that.

Most oils labelled "synthetic", "semi-synthetic", "part-synthetic", "synthetic blend" etc are only "cracked" petroleum oils with some exceptions.

0w oils normally contain "PAO\'s" because petroleum oils simply cannot meet the -35 degC pour point required to pass API\'s or ACEA\'s tests.

5w oils can just about be made with petroleum oils although it is common to put a small amount of synthetic in to pass the -30 degC pour test.

So basically some 5w\'s, and just about all 10w, 15w and 20w oils are petroleum based.

The noteable exceptions to name a few are Redline, Silkolene, Royal Purple, Motul, Amsoil and Fuchs although these companies all produce a different range of hydrocracked and mineral oils which are normally half the price of the true synthetics.

This is a general rule, price is a good indicator though.

Cheers
Simon

[wiggy]

So when yourefered to Mobil before did you mean the 0W40 they do? I have always used the 10W50 motorsport stuff they do so would this be good/bad in a rotary???

Also, whats the best Motul stuff to use, if this is currently in my car I will probs carry on using it

Thanks

[88GT-R]

Thanks for the info, Simon. You covered the point on seal damage from using PAO`s and esters, but what would the effect be when using these base oils with the oil injection system? Is there any indication that the petroleum based oils burn cleaner than the Synthetics?
I use 2 stroke oil as premix and have recently started using 10w60 "fully synthetic" oil produced in Germany. Would this be a true synthetic, and what sort of base would it be?
Many thanks,

John
88 GT-R

[oilman]

Originally posted by wiggy
So when yourefered to Mobil before did you mean the 0W40 they do? I have always used the 10W50 motorsport stuff they do so would this be good/bad in a rotary???

Also, whats the best Motul stuff to use, if this is currently in my car I will probs carry on using it

Thanks

I think you\'ll find it\'s 15w-50 and if it\'s Mobil 1 then it\'s poly alpha olefin basestocks so in theory shrinks seals. However as I stated above, I know of many people using proper synthetics with no problems.

The Motul range is as follows:

300V (Double Ester/PAO Fully)
8100 (PAO Fully)
6100 (PAO Semi)
4100 (Hydrocracked)
4000 (Mineral)
2000 (Mineral)

Cheers
Simon

[oilman]

Originally posted by 88GT-R
Thanks for the info, Simon. You covered the point on seal damage from using PAO`s and esters, but what would the effect be when using these base oils with the oil injection system? Is there any indication that the petroleum based oils burn cleaner than the Synthetics?
I use 2 stroke oil as premix and have recently started using 10w60 "fully synthetic" oil produced in Germany. Would this be a true synthetic, and what sort of base would it be?
Many thanks,

John
88 GT-R

John,

Synthetic oils actually burn cleaner than mineral oils as the molecules are of a uniform size.

I\'m guessing that the 10w-60 is Castrol RS which is a "hydrocracked" oil if this is the case. The premix is more than likely a synthetic if it\'s a bike oil.

Cheers
Simon

[88GT-R]

Hi Si,
The oil is not Castrol... It begins with an Mog... I can`t remember, and i can`t look as i am in Cyprus for a while:D

John
88 GT-R

[andrewrx7]

Interesting reading, Mr Oilman!


So here\'s a question....API specifications on the back of the oil cans.....are these worth taking any notice of? I\'ve always tended to buy oils that have the highest API ratings. Do oils have to pass specific tests to achieve a specific rating.....and if they do, is this an indication of the quality of the oil?

Cheers,
Andrew

[oilman]

Thanks!

API Specs. You\'re doing the right thing. Current is SL so look for this as all specs are backwardly compatible.

These are them:

API = American Petroleum Institute
S = Service - Petrol Engine Performance
C = Commercisl - Diesel Engine Performance

PETROL

SG - Introduced 1989 has much more active dispersant to combat black sludge.

SH - Introduced 1993 has same engine tests as SG, but includes phosphorus limit 0.12%, together with control of foam, volatility and shear stability.

SJ - Introduced 1996 has the same engine tests as SG/SH, but phosphorus limit 0.10% together with variation on volatility limits

SL - Introduced 2001, all new engine tests reflective of modern engine designs meeting current emmissions standards

DIESEL

CD - Introduced 1955, international standard for turbo diesel engine oils for many years, uses single cylinder test engine only

CE - Introduced 1984, improved control of oil consumption, oil thickening, piston deposits an wear, uses additional multi cylinder test engines

CF4 - Introduced 1990, further improvements in control of oil consumption and piston deposits, uses low emmission test engine

CF - Introduced 1994, modernised version of CD, reverts to single cylinder low emission test engine. Intended for certain indirect injection engines

CF2 - Introduced 1994, defines effective control of cylinder deposits and ring face scuffing, intended for 2 stroke diesel engines

CG4 - Introduced 1994, development of CF4 giving improved control of piston deposits, wear, oxidation stability and soot entrainment. Uses low sulphur diesel fuel in engine tests

CH4 - Introduced 1998, development of CG4, giving further improvements in control of soot related wear and piston deposits, uses more comprehensive engine test program to include low and high sulphur fuelsSG - Introduced 1989 has much more active dispersant to combat black sludge.

One point about API specifications.

API specifications are minimum specifications for oils. They exist for your safety so that you have reasonable assurance that an oil will "adequately" protect your engine. However, these are not, by any means, a standard by which you could determine whether an oil was good or not.

As an example, you\'ll find that even a cheap oil which costs next to nothing will most likely carry the API SL rating. That should tell you something about how hard it is to attain that rating.

The other specs to look for are the European equivalent of API which are called ACEA. These are more stringent than API.

They are as follows.

ACEA Specifications
(Association des Constructeurs Europeens d’Automobiles)

ACEA ratings are prefixed with “A” for petrol, “B” for light or passenger car diesel and “E” for heavy duty diesel.

The current specifications are:

A1 Fuel economy petrol
A2 Standard performance level
A3 High performance and/or extended drain
A4 Reserved for future use in certain direct injection engines
A5 Combines A1 fuel economy with A3 performance

B1 Fuel economy diesel
B2 Standard performance level
B3 High performance and/or extended drain
B4 For direct injection car diesel engines
B5 Combines B1 fuel economy with B3/B4 performance

E1 Non-turbocharged light duty diesel engines
E2 Standard performance level
E3 High performance and extended drain
E4 Higher performance and longer extended drain
E5 High performance and long drain plus API performances

Too much deatail but anyway, at least you know now.

Cheers
Simon