Author Topic: Oils, a technical explanation!  (Read 7708 times)

Offline oilman

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Oils, a technical explanation!
« on: June 02, 2005, 05:11:42 PM »
I have seen a few oil posts on here recently and thought that I would share my expertise. I have posted this before but thought that it was worth reposting in case you missed it first time around.

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
oilmans website:http://www.opieoils.co.uk
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the lemster

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Oils, a technical explanation!
« Reply #1 on: June 03, 2005, 09:11:45 AM »
yet more great information...

one question..

I have a 93 rex standard build no mods, I use halfords enhanced mineral oil 10/40

would you suggest I use something different? or, is this perfectly ok to use. I am due an oil change soon ( well 300 miles ago I change it every 3000 miles and filter) and would just like to know what other choices i have... woud you suggest I upgrade the filter aswell, or is this not your area?...

cheers and keep up the good advice

Offline oilman

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Oils, a technical explanation!
« Reply #2 on: June 03, 2005, 11:35:35 AM »
I would be inlcined to go for a good quality 10w-40 semi synthetic to get the best results.

Cheers

Simon.
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Offline Oedipus Rex

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Oils, a technical explanation!
« Reply #3 on: June 03, 2005, 11:55:33 AM »
Can someone sticky this pleas3e, as it is one of the most informative posts I\'ve read on this forum.

the lemster

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Oils, a technical explanation!
« Reply #4 on: June 03, 2005, 03:37:43 PM »
ok I will see whats out there and try maybe silkolene or I have heard shell helix get quite good write ups...

any particular one you suggest?...

Offline oilman

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Oils, a technical explanation!
« Reply #5 on: June 03, 2005, 10:36:06 PM »
Personally I rate Silkolene and Motul Oils for their quality.

You can always email me for a price list sales@opieoils.co.uk or catch up with me at JAPSHOW, GT BATTLE, JAE, TOTB etc etc.

Cheers
Simon
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Offline stu0x

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Oils, a technical explanation!
« Reply #6 on: June 04, 2005, 12:31:52 AM »
Very informative post, even if most of it did go straight over my head :)

The way I think about it, didn\'t Rotaryart do a group sell of Royal Purple fairly recently? And isn\'t Royal Purple synthetic? Which suggests that at least this particular synthetic is perfectly okay to use with a rotary.

Offline oilman

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Oils, a technical explanation!
« Reply #7 on: June 04, 2005, 10:28:26 AM »
As explained above, the word synthetic means nothing unless it is qualified.

What basestock is Royal Purple made of would be my first question and what are the percentages?

I don\'t know the answer to this although I do have some chemical analysis on a 10w-40 oil of theirs done in April 05.

It was a mineral oil with about 8% ester content and not a fully synthetic pao/ester.

You need to ask the right questions and don\'t take the statement "it\'s FULLY SYNTHETIC" on face value. Always ask what is meant by that, what are the basestocks and what group are they.

Here\'s an explanation.

Basestock categories and descriptions

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.  

Cheers
Simon
oilmans website:http://www.opieoils.co.uk
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the lemster

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Oils, a technical explanation!
« Reply #8 on: June 09, 2005, 07:11:12 PM »
dam you know your s**t

luckily I did chemisty at school ( even if it was nearly 15 years ago) so am used the names and structure of thing...

but even so

dang

Offline oilman

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Oils, a technical explanation!
« Reply #9 on: June 10, 2005, 09:30:17 AM »
Thanks for the compliments. I guess my user name says it all ;)

Cheers
Simon
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Offline Zimmy

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10W30 vs 10W40?
« Reply #10 on: July 14, 2005, 05:00:17 PM »
Does anybody know which is best for my FD?
It only has 12000 miles on it and is an American import. The manual says 10W30 (mineral only), but thats harder to get here. The last owner took it to a local Mazda dealer and they put in Shell Helix 10W30. Can\'t see that in the shops though.

I was going to put in Castrol GTX 10W40 after reading these forums, but could it be too thick (viscous) for a low miler?  :confused:

Also, any preferences for oil filters? The Halfords one doesn\'t seem any cheaper than one from the dealer (a few years back).

Z
\'95 FD

Offline oilman

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Oils, a technical explanation!
« Reply #11 on: July 14, 2005, 05:08:09 PM »
5w-30 is easier to get hold of and the difference is merely cold crank viscosity. Either that or a 10w-40.

Use a semi-synthetic as it\'s petroleum based anyway (not proper synthetic basestocks)

I use Silkolene/Fuchs XTR 5w-30 in my RX8 (it\'s a semi-synthetic)

Cheers
Simon
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Offline Jono FD3

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Oils, a technical explanation!
« Reply #12 on: September 01, 2005, 06:25:53 PM »
I\'m using Castrol GTX 10-40 at the moment just as a flush realy.....
what would you recomend I use??? The car has done about 45000 and runs like a watch with no starting problems (Hot or Cold)
Could you give me a name please as I dont understand all this pollycrack stuff justs plain basic oil names please!!!

Thanks for your help,
Jono

Offline oilman

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« Reply #13 on: September 01, 2005, 06:30:35 PM »
No problems, try Silkolene XTR 10w-40 or Castrol Performance 10w-40 or Motul 6100 10w-40.

If you\'ve no hang ups with using a synthetic then Silkolene PRO S 5w-40.

Cheers
Simon
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Offline Zimmy

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Valvoline 10W30
« Reply #14 on: September 01, 2005, 09:32:00 PM »
I ended up using Valvoline Turbo V 10W30 with a Blueprint filter I got in a local parts place.
Seems to run just fine and has hardly gone down at all after 450+ miles.

I\'m sure 10W40 would be OK too though especially with higher mileage.
Its the regular changes that are important I think.

Z
\'95 FD