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MARTIN WILLIAMSON of NORIA UK answer's your Frequent Question on Oils & Fuels!

An explanation on Oils:
Categorising and selecting an oil:
FAQ’s on your motor oil and fuels:
About the author:


What is oil?

Oil in its simplest form it is a mineral base stock derived from crude petroleum.  Additives are then added to the oil to enhance, suppress or impart new properties to the oil. 


What function does oil provide in my car or engine?

  • Wear control to minimise surface damage to components.

  • Friction control to reduce the power loss when surfaces move against each other.

  • Corrosion control to minimise corrosion and rusting of surfaces from acids and moisture in the oil and the environment.

  • Temperature control to remove heat from the working surfaces and components.

  • Contamination control to stop deposits on surfaces and hold particles in suspension and allow them to be removed by the filter.

  • Power transmission to support loads or transfer power from one point to another such as on the brakes.


Can these properties all be dealt with by a simple oil?

To a degree, but for superior performance required of modern equipment a better base stock and superior additive package are required. 


Why is engine oil so much more expensive than industrial oils?

Mainly because the oil is subject to extreme conditions in an engine compared to other mechanical systems, so requires a better base stock and additive package.  This is why the oil is not only more expensive, but generally will not last as long as say a gearbox or brake oil.  The additive package can form up to 30% of the volume of engine oil compared to just 1-10% of other oils. 

There is also the issue that commercially; up to 50% of oil sales are to the automotive industry. 


What are the differences between base stocks?

Base stocks are either mineral based, semi-synthetic, synthetic or vegetable based.  Most motor oils were mineral based until the last decade when Synthetics became available.  Synthetics are derived by a different refining process to offer superior performance. 


What are the advantages of Synthetics over Mineral oils?

  • Superior wear control

  • Superior friction control

  • Superior thermal stability

  • Superior aging characteristics

  • Superior film strength

  • Reduced fuel consumption

  • Improved power output through reduced friction losses

  • Improved detergency capability to reduce depositing on surfaces and maintain contamination control


Why don’t manufacturers use Synthetic oil?

Basically, synthetic oils cost as much as 3 times the cost of mineral derived oils.  However, a new engine requires a mineral based or semi-synthetic oil to allow the engine to break in properly. 


Oil Aging and Degradation:

Why do I need to change the oil?

There are various reasons that an oil needs to be changed periodically, but a lot depends on the driving style as to exactly when it needs changing.  For simplicity, most manufacturers suggest 12k miles or once a year.  Oil will age irrespective of whether it is used or not.  In fact, short trips in cold weather will harm the oil more than extended motorway trips will.  Extended journeys allow much of the harmful build-up of moisture and acids to evaporate from the oil. 


Why does my oil go black just after I change it?

Firstly, engine oil is designed to hold very fine particles of material in suspension.  It has a dispersancy package that keeps the particles finely suspended and stops them clumping together to form larger harmful particles.  These particles maybe fine wear debris from the component surfaces, or possibly ‘soot’, very fine carbon particles from the combustion chamber that gets past the piston rings through blow-by on the combustion stroke.  If you look closely at the oil, you will see the very fine particulate in the oil.

The oil going black was always a sure sign that the oil had a good detergency and dispersancy package.  However, on newer engines with tighter clearances and modern oils, there is less of this effect occurring so it will stay clearer for longer.



If I drain old oil from my engine, it seems thick and black, why?

Oil, like fine red wine, ages and oxidises.  The process of oxidation is naturally occurring in the oil, but the rate at which this happens depends on the following factors:

  • Temperature – the higher the temperature, the shorter the oil life

  • Moisture – the more water present the faster the oxidation rate

  • Oxygen – the more oxygen from low oil levels the faster the oxidation rate

  • Catalytic reactions – most typically from copper wear debris particles

As the oil oxidises, there are two parallel problems arising. 

Firstly, as a result of the oil molecules reacting and clumping together, the oil becomes thicker and darker. 

Secondly, a by-product of the oxidation is the formation of acids, which increases the risk of corrosion of component surfaces.  Examine an old engine and look at the chemical damage that is visible on the surface of the component.

Remember that when you drain an engine, there is as much as 20% oil remaining residual in the block, and just 10% residual of the old oil will damage the new oil instantaneously.  So if you have missed a service, have the oil changed, then run the engine for some time and then change the oil again.


What are the typical additives in my engine oil?

Additives are usually chemicals dissolved within the oil and act on the contaminants and components rather than on the oil itself.  They either coat the surfaces of the components or surround the particles or droplets of acids or moisture.

These additives are typically:

  • Anti-friction - such as AW or Anti-Wear or animal fats as friction modifiers to reduce friction between two components in direct contact (such as cams and followers)

  • Detergency to keep surfaces clean, and often formulated with an alkaline or base to combat acid build up in the engines, especially so on diesel engines, where fuel dilution can lead to sulphuric acid.

  • Dispersancy to hold contaminants in suspension

  • Corrosion and rust inhibitors

  • Anti-foaming to help release air bubbles quickly

  • Anti-oxidants to minimise oil aging

  • Pour point depressants to stop the oil going waxy or semi-solid in very cold climates.

  • Viscosity Index Improvers for Multi-grades (see later)


What does EP mean on a transmission oil?

EP stands for Extreme Pressure, and is like an AW or anti-wear additive, except that it is formulated for extreme loading.  It is often a sulphur phosphorous base, hence the distinctive smell, and will attack yellow metals such as copper or bronze.  Therefore, restrict its use to the differential only, and avoid use in a gearbox with synchro-mesh rings unless otherwise stated by the manufacturer.



What about these aftermarket additives?

The whole basis of their claims is around a graphite or Teflon suspension in the oil, which acts as an additional lubricant. With graphite, think of a deck of cards. Place a load on top of the cards and it will support it.  Place a side force to the load, and the pack or deck of cards will slide out. In other words, graphite can supposedly support vertical loading whilst allowing reduced friction. The main point where this applies is in the bearings in the crankshaft.

Other forms of solid lubrication include Molybdenum Disulphide and Teflon. In all these cases, it is a largish additive in the oil. To put it into perspective, the additive size is about 0.005mm. Your engines filter is approximately rated at 0.02mm in size.  The filters will either remove much of these solid suspensions in your expensive oil or, the suspension will settle to the bottom of your sump.

In theory, this looks attractive, but in practice they have been known to clog oil ways and filters. Some of the claims look attractive, but I often see no supporting evidence. In fact several years ago the FCC in the US slapped Slick 50 with a $10 million fine for false advertising. They were unable to prove their performance claims of less wear and more reliable engine performance compared to motor oil alone. I regularly hear stories about how someone has driven 50 miles on a dry engine etc. but, personally, I have yet to have seen their evidence, (call me cynical!).

There have been many independent studies on Slick 50, the most noteworthy include the National Research Council in Canada and South – Western Research Institute under the sponsorship of GM. None of these studies have found benefits and many have found drawbacks. Typical drawbacks reported in the literature and users include:

  • Settling and agglomeration of the solid additive particles

  • Filtration of the solid additive particles. (Some suppliers recommend not using a filter finer than 0.020 mm rating)

  • Restricted flow in oil ways and mechanical movement.

As with all aftermarket additives there are the usual problems such as:

  • Warranty of lubricant becomes void when aftermarket additives are mixed in, and some car companies will not honour the warranty, and believe me, if it came to court, it would be very easy to prove had been used.

  • Additive incompatibility with your existing oil. This of course relates to doping up with additive rather than buying a fully blended product.


What is Viscosity?

Viscosity, by definition, is an oil’s resistance to flow and shear.  Water is a low viscosity fluid; syrup is a high viscosity fluid.  Oil, like syrup, is a Newtonian fluid that, as you increase the temperature, the viscosity lowers, meaning it flows faster, or more easily. 


What is Viscosity Index (VI)?

It is the rate of change of viscosity between two temperatures.  The lower the VI, the more the drop in viscosity as the oil warms up.  The higher the VI value, the less the drop in viscosity as the oil warms up. 

Generally this is modified by the inclusion of additives to form multi-grade viscosity oils.  Synthetics usually have a higher viscosity index (less viscosity change against temperature) than mineral oils. 


What is the importance of viscosity in my engine?

The viscosity will determine how easily the oil is pumped to the working components, how easily it will pass through the filter, and how quickly it will drain back to the engine.  The lower the viscosity the easier all this will happen.  That is why cold starts are so critical to an engine because the oil is cold, so relatively thick.

But, the lower the viscosity, the less the load the oil can support at the bearing on the crankshaft.  The higher the viscosity, the better the load support.  Even this, however, has a trade-off, since the higher the viscosity, the more the drag at the bearing, and hence, potential power loss.  So a compromise is chosen to minimise power loss, but maximise load support.  Stick to the recommended viscosity for your engine.

For domestic use, engine life is important.  For motorsport, engine life is not critical, winning is, so these high performance engines use lower viscosity oils to maximise power output to the wheels. 


How is viscosity rated on an engine oil?

The Society of Automotive Engineers (SAE) developed a scale for both engine and transmission oils.  The measurement is undertaken in a laboratory in accordance with the American Standards and Tests Methods (ASTM) and is usually rated from 0 to as high as 60 for engine oils and from 75 to 100 for gear oils.  A 40 engine oil has a similar viscosity to a 90 gear oil.

Typical steps are 0W, 5W, 10W, 15W, 20W, 30, 40, 50 60 for engines and 75W, 80, 90 and 100 for transmissions. 


What is a multi-grade oil?

Until the early 60’s, most oils were a mono-grade, typically either a 30, 40 or 50 grade viscosity.  The higher the ambient temperature, the higher the number used.  This did mean that a cold start could be quite damaging for an engine, so in Winter, the oil would have to be drained and replaced with a lower viscosity oil.

Multi-grade oils were developed to allow year round use.  They are typified by a two number system with a W.  For example, 10W30.  The first number refers to the viscosity of the base oil used, and W is generally understood to mean Winter (although some suggest W for Weight of the base stock).  To achieve a useful viscosity at operating or warm temperatures, the 10W has additives (also known as Viscosity Index Improvers), which are like tightly wound coils that unwind as the oil warms up.  The expanding coil causes the viscosity to increase and perform like a thicker oil.  However, over time, these additives become susceptible to shear and lose some of their performance.

Historically, with older engines having looser clearances, and especially in the Mini/1100’s with the gearbox in the sump, these engines still generally require a thicker oil such as a 20W50 or 15W40, unlike modern cars which run on 10W30 or even 0W30. 


How are oils regulated or compared in the industry?

The American Petroleum Institute (API) categorises the formulation of oils according to a standard.  Typical engines of the period are used as a test bed, and a number of tests are run to ascertain the performance of an oil under test.  If it meets or exceeds the parameters of the test then it can be classified in that category.  However, oils in the same category do not necessarily have equal performance, they may only meet, not exceed, the requirements of that category.  Current ratings are based around standard engine design of the moment, so modern oils are designed to withstand higher power outputs, with multi-valve and overhead cam etc reaching higher rpm than previously. 


What are these categories?

For petrol or Spark Ignition engines, there is a ‘S’ rating, and for diesel or Compression Ignition engines, there is a ‘C’ rating. 


Spark Ignition Oils:

The ratings started in the 50’s for typical engines with an API SA rating.  By the 70’s it had moved onto an API SC rating.  During the Nineties it rapidly moved up to as high API SL.  The oil required will depend on your driving needs, i.e. daily commuting versus track-day or motorsport stuff.  For the latter, the best you can afford, but for commuting, an API SH or API SJ should be more than adequate.  For older engine designs, avoid the very latest API spec, use one that is designed for that design of engine, such as an API SF. 


For Compression Ignition Oils:

The API classification is currently at API CI-4, although this is designed for exhaust gas recirculating (EGR) engines where the soot loading is consequently higher as a result of remixing the emissions into the air intake.  Again, the rating has moved on rapidly during the 90’s, and the same comment applies for spark ignition, that is, buy the best you can afford.  For fleet use in off-highway equipment, the way to extend the oil drain interval is to go for this API CI-4 oil.   


Where can I find the API rating?

The API rating is usually shown in a doughnut or circle on the side of the oilcan, or may be listed in the small print.  Not all manufacturers show this on their containers, possibly for the reason that not many people know what it means, or more cynically, because it hasn’t been fully tested!   


Is a major brand better than a smaller, unknown brand?

Don’t be taken in by marketing; check that an oil is a fully synthetic as some claim to be ‘synthetically engineered’ whilst only being a semi-synthetic.


In independent testing that I have been involved with in the past, there have been significant differences in wear control between major brands, and don’t write off smaller brands, either.  Some smaller brands specialise in a type of oil and do not carry the overheads of a major supplier.  They dedicate their facilities to a type of base stock, operate in a cleaner manner, and use higher quality base stocks with specifically formulated additive packages.  But it will cost more.


One such example is Royal Purple, used predominantly by the motorsport fraternity, with good reason.  Actual evidence has shown their oil to cope with the stresses imposed on engines such as the Subaru Impreza and Smart where major brand oils have failed. 


What About Brake Fluids?

Dot 4 and DOT5.1 is ester based and is hygroscopic, that is, it absorbs moisture from atmosphere. Along with high temperature abuse, the moisture reduces performance of fluid and lowers boiling point from around 450°C to about 150°C. So..............run a track day or pull a caravan and you work the brakes hard, thus fluid starts boiling fairly quickly!  Boiling means bubbles which means compressibility and spongy or zero power transfer to the slave cylinders.  Water absorption (through the rubber hoses and seals) also leads to rust in the slave cylinders and consequent pitting and leakage past the seals.  So change the fluid every two years or sooner as per the recommended interval.

Dot 5 is silicone based, or also known as synthetic, and although more viscous leading to slightly less responsive brakes, it doesn't eat paint work, doesn't absorb moisture and can run to extreme temperatures, and only needs replacing every 3 years as opposed to every year with Dot4.

And if you open a Dot 4 bottle, notice it has a foil seal. Use what you need, then chuck the rest away, because on the shelf, in the average garage, without the foil seal, it will be useless within 30 days having absorbed so much moisture.


And if you want maximum transfer of power to the wheel cylinder, consider braided hoses, which minimise bulging and thus a loss of power transfer. 


And as for Shell Optimax fuel!

Optimax offers the following because of a better burn capability and a higher RON number 98, compared to other super unleaded fuels of RON 97:

  • Better fuel consumption

  • Better power output (probably 5% max)

  • Better, cleaner emissions from the exhaust

  • Maintains a cleaner fuel system (pipes and injectors, as well as in the combustion chamber minimising depositing)

If you have a knock sensor that can adjust the engine management/timing, then you will see all 4 benefits. Unfortunately, the standard K series does not so most people don't notice the improvements in the short term.  The KV6 does benefit so I use it regularly. Still on the 4 points above, it is difficult to justify the extra costs.

On the K series, I use it in the wife's 214 in the hope that at least points 3 and 4 are a benefit. She does a lower mileage than I do, so it doesn't cost as much for this 'insurance' policy and doing my bit for the environment.

Don't expect immediate benefits from it, you need to use it regularly to see the advantages. If your car has suffered from poorer quality fuels over a year or more, then several tanks will help you recover lost efficiency through clean up, not increase performance per se, unless you have the engine management system to cope.

You could talk to your garage about adjusting the timing to benefit from it if you use it regularly, especially on an older car.

If you plan to keep the car long term, then invest in a good quality fuel and oil and stick with them as the reduces long term problems. If you plan to sell in next couple of years, then don't bother too much.


If you’re seeking ultimate power, then an additive in the fuel can help raise the RON to as high as 100 with Optimax, but you will need to ensure the timing is set up for this gain.


I would like to know whether for NORMAL driving it’s worth the added expense of using semi-synthetic or synthetic oils?

If you plan to keep your car for more than 5 years then go for best you can afford. That means synthetic, not semi-synthetic.

For 3yr/60k operation, use what's recommended and then let the next owner worry about it!

Seriously, if you plan to maintain a Full Service History by having a dealer service for a 3yr/60k ownership, then let the dealer put in what they will, it should be the approved stuff.

Going for fully synthetic will mean dumping oil at 15k miles that may still be good for another 10k if you do a lot of motorway miles. If you plan to run the car into the ground over next ten years or until Labour say no more, then buy the fully synthetic, it will help maintain optimum performance (along with good quality fuel like Shell Optimax to keep the injectors and engine clean).


I believe Castrol Magnatech or any other semi-synthetic is a good choice from the point of view of cost versus protection for the average owner. Shell Helix Ultra is the top of the range of the Helix brand and is fully synthetic like Mobil 1. But these two are expensive at 50% more in cost I believe.  


I do occasional track days, too, what should I use?

There are a couple of other smaller specialist oil manufacturers such as Molykote or Royal Purple who, in fact, use purer base stocks that are less susceptible to shearing and provide a greater film strength through chemical action rather solid action. These are proven case studies, the motorsport people use Royal Purple and independent assessment has shown better wear protection than even oils like Mobil 1. 


Are frequent oil changes better?

Many people still believe that frequent oil changes are the best way to look after an engine, which is true if you do the oil change while the oil is still warm as it drains out wear debris material from the system. If you are looking to extend the oil drain interval, then a fully synthetic is a better choice to minimise harm from premature oil failure. Standard mineral and semi synthetic oils offer satisfactory protection but be warned that they do not always last the service interval (depending on your style of driving).

What type of oil does the factory use?

Texaco-Havoline 10W/40 semi-synthetic and then recommend the 'Extra' fully synthetic MGR Approved stuff for MG’s and Rovers after 15K miles. 


My engine is modified, should I deal with it differently?

Your engine will be stressed a little more than the standard anticipated design usage. For safety, extended reliability and reduced wear rate, a superior oil should be used to counter the effects of the modification work.  Essentially, the higher film strength of a synthetic will reduce the impact of the increased loading from the extra modifications.

Film strength is the ability of the oil to support a load without metal-to-metal contact between the components, the biggest cause of wear on your bearings! It is generally accepted that 80% of the wear occurs at start and shut down. The other 20% occurs in oils diluted with acid build-up, moisture and fuel, or high load at peak RPM.


Film strength at the bearing is dependent on the oil's capability to resist shear at the bearing.  Some of the best oils are expensive but do offer significant protection despite being a lower viscosity. This lower viscosity reduces friction from the oil at the bearing thus allowing more power to be transmitted to the drivetrain. This kind of oil finds favour with motorsport people who are seeing very good engine life and oil life during a hard racing season.

When oil first goes into service, it will find a balance in the engine as the molecular structure accommodates itself to the engine. It is a little thicker at this point so needs time to settle before being loaded in anger/competition.

Should I keep this oil in until the next service schedule and just top it up for now?  In another words, can I mix oils?

Being pragmatic, I say better to have the right level of oil than worry about the mixing effects over time.

Why is Idling bad for my engine?

Particularly on diesels, idling will not allow the full combustion to take place, so wet fuel remains in the cylinder and starts to run down the bores. This will reduce the wear control from the oil splashed up onto the cylinder walls, and further, will accumulate in the oil, lowering the viscosity and reduce additive effectiveness such as the dispersancy additive, causing larger particles to increase wear rates. In some cases the dilution can become dangerously high (>5%).

So, start your engine, and move off.  

Running in a new Engine

To minimise future oil consumption problems, it is advisable to take it easy during running or bedding in.  Some people suggest town driving is best, and to avoid constant revs in the same gear. On this motorway issue, I had no choice, I had to travel to London to see a client, so I used the slow lane, and drove between 55 and 70 mph, and also shifted gears a few times. And believe it or not, deliberately planned to take in as many road works as possible to force speed and gear changes. At 17.5 k, I have no oil consumption, but I changed the oil at 3.5k to remove bedding in debris etc and also had filter changed.


Avoid synthetic oils during running in, a change at 1000miles would be too soon for this, 10k miles would be better. Some manufacturer’s use a running-in formulation which may have certain chemical advantages, but I can't see it having an impact on the wear debris generated during this period, which itself will create further wear if not removed soon. Viscosity has an affect on the drag and the oil film, so optimum viscosities must be maintained to avoid excessive power loss, or reduced film strength and resulting wear. Multi-grades will suffer some shear down in use (losing viscosity) and may be thinned by fuel dilution in the bedding in phase. Oil will also oxidise in the presence of higher temperatures, oxygen and wear debris, resulting in a thick, highly acidic oil. Hence my concern at offering the first service at 15k miles, although fortunately I do a lot of m/way miles.

From research I am involved with I know that wear can be radically reduced through finer filtration, and that automotive filters are not rated in the same way industrial filters are. From testing at a certain site, we found an average 5BHP more on cleaner engines after 900hr endurance testing. Since wear will influence fuel economy and emissions, as well as oil consumption, I am keen to practise what I preach in my training and consulting, so I will investigate breather and filter options in addition to the oil filters



Switching to a Synthetic on new and used cars

DO NOT USE a fully synthetic until the engine has covered a little more mileage (approx 10k) because the engine is still bedding in for some time up to this point. Then switch to a Shell Ultra Helix or Mobil 1. What are the benefits? Less wear, less power loss in the engine, better fuel consumption.

Generally, the reference to synthetic oil for an engine means a lubricant is formulated with a polyalphaolefin (PAO) base oil. PAO, which is often called synthesized hydrocarbon, is pure and is compatible with mineral base oils.

However, because the PAO base oil does not dissolve additives effectively, it is usually formulated with an ester co-base (usually di-ester and/or polyol ester). The additives are soluble with the ester and the ester is soluble with the PAO.

Likewise, the PAO tends to cause seal shrinkage and the ester causes seal swelling, so the effects are offset when both base oils are present.

When switching to a fully synthetic on an older engine, or one with a higher mileage, it is the ester that can cause problems when one changes from mineral to synthetic. Ester base oil used alongside PAO base oil in lubricant formulation has excellent natural detergency. In other words, it will clean up deposits on component surfaces as a result of thermal and oxidative degradation of the lubricant. When one switches from typical mineral-based engine oils to a typical synthetic-based oil, the varnish layer will be removed by the ester in the synthetic oil and become suspended.

This suspended material can rapidly clog filters and can block oil flow passageways and lead to component starvation. The same is true for gearboxes and other industrial machines. So think twice about switching to synthetic oils in applications where the engine or other machine has been operating for some time with mineral oils.


On rebuilt engines of the older type, such as MGB, the same applies, allow for bedding with a standard oil, and then switch to a synthetic, although there is some concern that the higher detergency will not allow a beneficial depositing and as such, the oil consumption may prove a problem.



Is there an easy way to check my oil?

Check this link:

Noria's Practicing Oil Analysis article on the Blotter Spot Test

Seriously, avoid running high speeds and switching off immediately, give it a cool down period in the last few miles, let the oil warm up properly, about 10 miles (even if the temp gauge is up to position, it takes a while longer for the oil to hit temperature).

The linked article has a few other comments on driving habits and things to avoid. 


Why is it important to have clean oil in my engine?  Can I actually see the particles that are most damaging?


An article on cleanliness of oils and fuel consumption.

Noria's Practicing Oil Analysis article on engine oil cleanliness



How do I do an oil change properly?

Generic topic on the best practices of doing an oil change:
Noria's Machinery Lubrication Article on Oil Change




Martin Williamson (aka MartinW), a mechanical engineering graduate from Cape Town University, is a technical consultant and company director involved with industrial oils with an unhealthy interest in automotive matters! Noria UK Limited provides training and consultancy to end users as well as in support of major suppliers of oils and filters.


His work has included research in the automotive sector including Formula One, Jaguar, Rover and Land Rover.  In South Africa, he was involved in oil analysis on off-highway diesel engines (16 cylinder, 16litre beasts!).  He currently runs an MG ZT, and is slowly restoring a 1980 MGB GT.

His automotive ownership is predominantly MG Rover, although there were a few Nissans in the past, but the list is as follows:

1973 Austin Apache (a weird Michellotti redesigned 1300, but prettier than an Allegro!)

1976 Datsun 180U SSS (like a 240z with 4 doors!)

1965 MGB Roadster

1992 Nissan Sentra (Sunny in the UK)

1987 Nissan Bluebird

1991 Mini 30

1994 Rover416 SLi

1998 Rover 420 SLi

1998 Rover 214 Si

1999 Rover 75 Club

2002 MG ZT 160+

1980 MGB GT


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