This article is written in response to the numerous queries I receive about oils and lubrication, it will highlight the main types of oil, the differences in oils, and hopefully remove many of the myths surrounding the marketing ploys of oil manufacturers. Intentions are simply to provide enough information about lubricating oils for people with little knowledge of oil to allow them to select the correct oil, inform people how oils work, and allow them the knowledge to buy the correct oil without being ripped off.
Engine oils are full of myths and bold claims, many believe the hype about synthetic oils, so let us establish the facts before we begin, all oil types contain mineral oil as it is this which lubricates the engine, nothing else. The all singing, all dancing fully synthetic oils are not totally synthetically manufactured as they contain mineral oil to do exactly the same job as mineral oils, they just do it differently.
Engines have to cope with many differing problems, this means the oils have to cope with these problems, and as engines continually improve, so do oils; this equally applies to transmission oils, power steering fluids, and any other vehicle fluid. The average engine generates several technical problems, we will begin by looking at these in more detail to understand the requirements and needs of an engine oil.
Engines need a film of oil to prevent metal to metal contact between various moving components, these may typically be steel to steel, but many other bearings or moving components may be a variety of other materials. Aluminium is increasing in engines to reduce weight, lead and indium are contained in many bearings, white metal is often used in bearings, and many rubber or synthetic rubber components are used in a variety of seals. Engine oil has to provide adequate lubrication for this variety of components without damaging them.
Engines operate by combustion, basically what is contained in the combustion chamber is fuel which either rapidly explodes if it is petrol, or burns more slowly if it is diesel, both fuels will dilute lubricating oil used to lubricate the cylinders. Combustion generates other problems, they both generate a variety of gases which are absorbed by the oil, and they form deposits which attack metal surfaces; in addition they form ash from burning micro particles which pass through the air filter, this is normal. These gases and various ash deposits are corrosive, and the residue needs to be removed and held in suspension by the oil until they can be naturally dissipated, filtered, or evaporated.
Engines contain working surfaces subjected to extreme loads, these loads are often so high that they exceed the highest loadings in a gearbox or axle, and both these components use EP or extreme pressure lubricants, so engine oil has to provide this also. Camshafts are the common high pressure area as the lobes contacting the valves have such high loading forces, but modern engines are increasingly being fitted with hydraulic tappets, these again are an extreme pressure area.
Lubricants have to cool, engines are running at higher working temperatures for improved thermal efficiency which translates into higher power outputs and increased fuel efficiency, and modern engines are increasingly fitted with more components. Turbochargers are a prime example, they work at extremely high temperatures and require more cooling capacity than actual lubrication, for this very reason a lubricant has to flow at high flow rates to cool as well as lubricate.
Lubricants suffer other attacks, these are often from sludge forming as metals cool, they condense water vapour from the air into water droplets, this has to be absorbed by the oil and held in suspension until the oil is hot enough to boil it off naturally. This is what leads to the mayonnaise we often find if the head gasket is gone and letting water into the oil, or if a vehicle only does very short journeys and the oil rarely gets up to full working temperatures.
The conclusion is simple, oil has to deal with lubrication and cooling, attacks from a variety of sources, be able to do all this while giving a good service life for our engine; and all without complaint and keeping up with modern engine developments.
What Is Oil
A simple question, but one which very few can answer! But the answer can be quite simple, the oil you buy in a container is comprised of only two major components, and these are the mineral lubricating content and an additives package. Mineral oil is just that, mineral oil; the additives package is a complex chemical package whose sole purpose is to protect the mineral oil content to allow it to perform the various functions required by modern engine oils.
To understand the relationship between the mineral lubricating content and additives package we have to understand how the additives work and what functions they perform, some additive components work alone, others work in conjunction with other additive components. This can be explained more simply if we move back in time to the earlier mono-grade oils previously used before the modern multigrade oils, and help us understand the paradox which arises.
Oils have always been measured in one of two measurements; these are the true measures of oils and lubricants as they cover everything from the crude oil in the ground to the thinnest crude oil derived product. These measurements are “Saybolt Universal Seconds” and “Centistokes” measurements and are the measurements used if you are a Texas oilman hitting a strike or a physicist developing oil products, many professional engineers, me included use these measurements.
Such measurements are too complex and wide ranging for automotive lubricants, but are fine if you have a need to work in such wide ranging measurements, so were simplified by the Society of Automotive Engineers (SAE) for ease of use. The SAE measurements still apply today and are often marked on a lubricants container and pertain only to lubricants used in automotive and vehicular applications, irrespective of if it is the average motor car, truck, and tractor or off highway plant. Many other engines used in other applications such as huge ships, aircraft, and many other applications which use internal combustion engines have adopted the SAE ratings for ease of use.
Early motor oils were mono grade, they used a low viscosity grade of oil in winter and changed this to a higher viscosity oil in the summer, and this is where the SAE ratings determine the viscosity of the oil. Viscosity is measured as a number; a low viscosity has a low number and is thinner for use in cold conditions as it allows easier cranking in cold climates, but lower performance at higher temperatures, and less effective lubrication at high temperatures. Higher viscosities have a higher number which denotes its performance at higher working temperatures, this explains why mono-grade oils were changed, and an SAE 10W was used in winter in cold weather and a higher SAE 40 grade was used in warmer summer climates.
If we transfer this knowledge to a multigrade oil we will see it comprises two numbers, the lower first number tells us how it operates when it is cold and the higher number tells us how it works when it is hotter. Therefore we can replace our two mono-grade oils with one oil, this would be shown as an SAE 10W/40 oil, and basically it removes the need to change the oil for differing working temperatures and replaces the two mono-grades with one multigrade oil.
This throws up our first paradox, we know a cold oil measured at 0 degrees centigrade is rated as an SAE 10, but as oil heats up it gets thinner, so how does it act like a thicker oil when it is actually getting thinner. This is where our additives package works, it simply allows the oil to replicate a thicker oil by using its most important additive, the Viscosity Improver or VI, and it is the viscosity improver which allows it to act as a thicker oil than it actually is. VI’s act by the heat activated modification of the molecular structure of the mineral lubricating content to develop them from tiny molecular particles to much longer strands, and these longer molecular strands are much harder to break down then single molecules. These give the additional protection and lubrication of a much higher viscosity of oil; it could be accurately said that our supposed multigrade oils are nothing more than simple thin mono-grade oil with replicating additives, this would be true.
But how do we deal with the other problems oil encounters? We look at the other major components in our additives package, these are:
Anti Oxidants work by improving the resistance to attack from the various oxidising agents within the engines environment, and these are predominantly the various combustion gases and fuels which the oil absorbs during combustion. Anti oxidants work as a stand alone entity in the additives package, and, in conjunction with other components of the additives package.
Corrosion inhibitors work by a variety of methods, these essentially protect the oil from the various other ashes which pass through the air filter as tiny solids and are burned during the combustion stage, they also work in conjunction with Anti oxidants.
Detergents are the cleaners of the oil as their name suggests, these work by taking the various gases and particles and move them to the sump where they are held in suspension in the sump until they are treated by other additives. Detergents allow larger and smaller solid particles to be held in suspension, from here they are filtered as they are passed through the oil filter, or they suspend microscopic pockets of gases in the oil until they can evaporate naturally from the heat of oil up to working temperatures.
Anti Sludge agents work by absorbing and isolating the condensation and water droplets, they work specifically with moisture and small burned particles and hold them as microscopic pockets of water on the surface of the oil in the sump. They also facilitate the easy removal of these tiny water droplets by chemically acting upon them and breaking them down, as the oil heats up to working temperature they are simply boiled off through the crankcase breather. Anti Sludge agents work in conjunction with Detergents, Viscosity Improvers, and Anti Oxidants to protect the oil.
Dispersants work in conjunction with Detergents, Viscosity Improvers, and Anti Oxidants, as well Corrosion inhibitors to break down the various solids, liquids, and gases contained and collected by the various additives package components. Breaking them down allows them to be more easily dispersed by a combination of passing them through the combustion stages, evaporating them off, and not allowing them to contaminate the mineral lubrication content as easily.
Now we have an understanding of how the additives package works, and how essential it is to maintaining the quality and protection of the mineral lubricating content of the oil, and allowing it to do its job for longer.
Now we need to look at the differing types of oil, there differences, and how they work in our engine, these oil types are mineral oil, semi synthetic oil, and fully synthetic oil. We will look at their differences and how and why they are selected for a specific, or family of engines; and what problems may arise from using the wrong oil within certain classes or types of engines.
Mineral Oil
Mineral oil is the oldest form of oil, and it gets its name as it comprises an average mineral lubricating content of around 55% and an additives package of 45% in a modern multigrade. The additives package is made purely from crude oil or organically sourced ingredients such as castor or rape seed, and both the mineral lubricating element and the additives packages are mineral or organically derived. Mineral oils have a thick film, or film thickness, this is usually around 1:10,000” thick, mineral oils have such thick films as the engine manufacturing machines and equipment were nowhere near as good as they currently are, this leaves large internal clearances. Having such large clearances means the oil film has to be thick as it has to fill these clearances to provide adequate lubrication. Film thicknesses are important as they have to be thicker film thicknesses than are actually required by the engine; the film thickness is then accurately controlled in critical areas such as the cylinders, by the oil control piston rings.
If the film thicknesses are to low the oil control rings would have nothing to scrape away and there would be inadequate oil to provide cylinder lubrication, in bearings it matters less as they take up what they want or need and the surplus oil runs away.
Mineral oils have the lowest working life of any of the oils, this is why the mineral lubricating content is higher than other types of oil, and the additives are the lowest amount of additives.
Semi Synthetic Oils
Semi synthetics are an improvement on the traditional mineral oils, this is due to the additives package improvements by synthetically reproducing a proportion of the compounds within the additives package. Replacing the mineral additives with a proportion of synthesised additives means a longer working life in a wider operating range than traditional mineral oils. Mineral lubricating content is lower than traditional mineral oils, and this typically averages around 45% mineral lubricating content with the remaining 55% being the additives package. Semi synthetic additives packages are simply a mixture of normal mineral derived additives and synthesised additives which are blended together to form the additives package, being comprised of mineral and synthesised additives offers better protection to the mineral content. Semi synthetics cost more than traditional mineral oils, this is due to the additional cost of producing the synthetic components of the additives package, but this makes them perform so much better and over a wider and longer working cycle. This invariably makes them more cost effective due to their longer working life. Semi synthetics have another little trick, the synthesised elements allow them to work in more modern engines with film thicknesses which are lower than traditional mineral oils which are demanded by newer engines with tighter internal clearances. They also have the capacity to run at thick film clearances in older engines, being able to run in newer and older engines makes them very versatile and able to be called “backwards Compatible”, backwards compatible means they are designed for both applications.
Full Synthetics
Full synthetics are traditionally known as the best oils, they differ from mineral and semi synthetic oils in their additives package, this is simply that their entire additives package is fully synthesised and contains no mineral content in the additives package. This allows the mineral lubricating content to be much lower, it can be as low as 15% mineral lubricating content, but is traditionally around 30% mineral lubricating content, with the remainder being the additives package.
Full synthetics also have the thinnest oil film thicknesses and are not backwards compatible, it is this very thin film thickness which creates problems if it used in engines which do not have the tightest internal clearances. This basically means the film thickness is insufficient for older engines with large internal clearances, and for this reason it must not be used in engines, particularly older engines which are not designed for operating on fully synthetic oils. Lacking the desired film thickness leaves all the operating surfaces short of oil and leads to bore scuffing where the piston rings come into contact with the bore itself as the piston and rings are not held in position due to a lack of film thickness. This equally applies to bearings such as crankshaft or camshaft bearings.
This is a common mistake people make, they believe the marketing hype and buy full synthetic oil, believing it to be the best, and then use it in engines not designed for it and suddenly within a short time the engine is trashed.
Oil Specifications
Oil specifications generally come in three types which are knows as SAE, API, and ACEA; it is prudent to understand these specifications and what they mean to us as consumers of engine oil, SAE ratings are already covered as these are basically the viscosity ratings. API and ACEA ratings are different, these are worldwide ratings and recognised everywhere, a typical API rating would be followed by two letters, ACEA ratings would be followed by a letter and a number, and these may differ between oils for petrol and diesel engines.
Typical API rated oil would bear the API rating API SH, and a typical ACEA rating for diesel oil would be ACEA B2, it is not necessary to fully understand the full meanings of them all, but to recognise what they are.
It is also essential to know the oil specifications your engine requires as this allows you to buy a quality of oil which is good enough for your engine, and to stop you paying excessively for a product which is far too good for your engine. Let’s look at a simple example. Daihatsu had the same engine in production for many years, it was the 2.8 Fourtrak diesel, which came as normally aspirated, turbo diesel, or turbo intercooled diesel; but these were basically the same engine in production for a long time.
We must also look at how new oils progress, years ago a new oil specification came out about every three years, now we have a new one every year, it is essential to remember that oil technology and specifications progress.
The original engine oil specification was API SD which was the oil of the time, it was the very newest and latest specification of engine oil, and it was the reason Fourtrak’s required it and they recommended oil changes of every 3000 miles. As oil technology improved, but these engines remained the same; the newer recommendation was for API SG specification oil as this was now the best due to advances in engine oil technology, same engine but with 6000 mile oil change intervals. So just knowing the oil specifications means we could buy an API SG rated oil and use it in earlier vehicles and increase the oil change intervals from 3000 miles to 6000 miles; so a cost saving from buying an API SG rated oil.
As oil technology moved on this latest oil is now a very old specification oil; prudent buyers may see oil on offer at many outlets very cheaply, our Daihatsu Fourtrak owner now knows what to look for and can buy this now cheap oil as it is API SG or higher. Knowing our engines oil specifications mean we become prudent buyers, if our engine requires API SG rated oil we would be wasting money buying a much superior API SP rated oil as it is far in excess of our engines requirements.
ACEA ratings are similar, these simply have two ratings, one for petrol engines and one for diesel engines, we simply need to know the engines oil rating requirement and check the containers specifications to see if it meets or exceeds our vehicle specifications.
One other form or rating is often printed on oil containers, this is a manufacturers rating, it may say meets the specification of Volkswagen XXX XX XXXX, or Mercedes Benz XXXXXX XX XXXXX, or maybe BMW XXXX XXXXX. These specifications are often designed to dupe the public and are best ignored, and it will be shown why later on.
Oil specifications are misleading for many other reasons, this is mainly due to the oils life cycle, basically the oil containers content is far superior to the specification shown on the container as this is the oil specification at the end of its life. To explain this we have to look at specific engines and see how it affects the oil as it is in service in an engine, and the manufacturers recommended oil change intervals. If we have an oil which is rated as API SJ and in a Ford road car engine with 10,000 mile oil change intervals, when the old oil is changed at the specified oil change intervals it will still meet or exceed the specifications of API SJ. We can logically conclude that the oil specification is its end of life specification, or minimum specification, the oil which went in might be rated as API SJ, but it is much higher to allow for it’s in service deterioration. In a Vauxhall engine our oil may have oil change intervals of 9000 miles, this is down to how the engine uses the oil as all engines are different, and it may be that our Vauxhall engine runs hotter than the Ford engine, or it produces more combustion emissions. Our manufacturer also works on the side of caution, in reality the oil may run for 11,000 miles in our Vauxhall engine, but erring on the side of caution makes the Vauxhall engine last longer, also the manufacturer makes more profit from more frequent servicing.
If we use the same oil in a 4X4 engine the manufacturer may reduce the servicing intervals to 6,000 mile oil changes, this is because many 4X4’s are used off road and are subjected to more abuse from heavier engine use, and more contamination from dust. We already know that minute particles are allowed to pass through the air filter and are burned in the engine, on an average road vehicle this is insignificant amounts, but it becomes significant on a 4X4 working off road in very dusty conditions. Dusty conditions mean more airborne dust particles, so much more fine dust will enter the engine, and the vehicle will basically have its oil changes reduced to compensate for this extra contamination, and to allow the oil to stay in grade. Many 4X4’s, plant, machines, boats, and other engined vehicles will have an arduous service recommendation; this is to counter any extreme conditions a vehicle will work in, any of these vehicles will work in hostile environments, so will have service intervals reduced to about half. It may be that our average 4X4 spends a lot of time working in water or very wet conditions, this means a proportion of water will enter the engine, this is not enough to cause physical engine damage, but it is significant enough to make the anti-sludge component of our additive package work overtime.
The Cons And Misinformation
Many oil manufacturers resort to slick marketing which is designed purely to dupe the consumer and is done in several ways, the most popular way is to introduce a technical element which is perfectly legal, but looks impressive.
One prime example is a well known oil manufacturer claiming “polarised molecules” which makes its oil sound grand and superior until we realise all liquids have polarised molecules, without it they would be a gas. Treacle, oil, urine, and water are all liquids, being liquids means they contain polarised molecules which are attracted to each other to form the liquid, if the molecules were not polarised we would have non of these liquids.
This is perfectly legal advertising as it is technically correct, it contains polarised molecules, so no lies are told, but it is the way in which it is presented which is designed to dupe the consumer into thinking it is a superior product.
Many people will see the current advertisements on the TV or in the media and know which product this is, and that it is expensive when compared too many other better products of similar specification.
Manufacturer’s specifications are a prime example of misleading the consumer into thinking a product is superior, many use terms such as, meets the specifications of BMW, Mercedes cars, Porsche, Aston Martin, and other premium car manufacturers. It may meet the specifications of these manufacturers, but the question we have to ask is, are these current manufacturers specifications? The answer is generally NO. The specifications from these manufacturers are often genuine, but very old specifications; it may meet a specification for a 20 year old BMW or a 25 year old specification for Mercedes Benz; so always view such specifications with suspicion.
Such advertising looks impressive on a manufacturers packaging, although it looks impressive as it is perfectly legal because it meets these prestige manufacturers specifications even though they are very old specifications. Basically it is legal because no lies have been told; it is simply that the whole truth has not been told as the specifications are genuine, just very old specifications, and designed to dupe the less knowledgeable consumer. This is nothing more than legally manipulating specifications to attract customers as prestige or specialised vehicles have superior oil specifications to other general vehicles of a similar age such as a bog standard ford, Vauxhall, Peugeot, or Fiat.
The moral is very simple, where claims are made just check them out; it is very easy with computers as many people have manufacturers oil specifications going back decades, so a quick check will reveal just how old they really are. Never be duped by slick marketing talk, obscure technical facts, and claims of meeting prestige vehicle manufacturer’s specifications unless you have checked them out fully.
Who Makes Oil
A simple question but who knows the answer? Do all the premium oil manufacturers make and sell the oil in their own names, no is the simple answer as many leading brands of oil are made by other non associated companies. One premium oil manufacturer who bought (allegedly) fully synthetic oil to the mass market do not actually make their own oil, another manufacturer makes it for them; all they do is have their own labels printed and sell it. This happens more frequently than many people realise, and is a good way of getting a top brand oil at rock bottom prices.
Many premium oil manufacturers actually manufacture their own brands of oil, others simply supply an additives package to another smaller oil manufacturer who just adds it to their mineral lubricating content, and others do not make their own oils at all. If anyone bothers to research who makes oil for which to brand they will turn up some amazing results, they can buy the same oil from the actual manufacturer under their own brand and have a top quality product at a fraction of the price.
Buying Oil
Now we have this useful information, we can use it to our advantage, we now know we need to find out two things about our vehicles engine, its SAE or viscosity rating, and either its API or ACEA rating or oil requirement. Oil technology moves on which means oils that were top class a decade ago are now the older budget oils, and are much cheaper then the latest oils, and are often found on sale or offer at a surprising range of non oil retailers. This means that these older budget oils meet or exceed our engines requirement due to the age of our vehicle.
Recently I noted some oil at a large DIY retailer and I wanted oil for an older vehicle, the oil specifications on the packaging were API SJ, 15/40. These exceeded the oil requirement for the engine in which it was to be used, so was perfect and cheap at £1.99 for 5 litres, on offer. They had 10 X 5 litre containers left, so I bought them all for the princely sum of £19.99, this left me with a bargain as I now have 10 oil changes worth of oil for less than £2 per oil change.
This is where knowing and understanding oil specifications pays dividends, if you spot any oil on offer at a bargain price, you can find out if it meets your engines minimum requirements simply by looking at the oil specifications. This enables you to get a bargain buy.
Many retailers use this type of misinformation to sell oil to a gullible and uneducated public, this often dupes them into buying a product which is far superior to their needs, obviously at inflated prices with larger profits for the retailer. If this happens you simply look at their range until you find something much cheaper which meets and exceeds your engines requirements and make a substantial saving from not buying excessively over specified oil. This has another benefit, if you use a regular retailer of car equipment and they know that you know and understand oil specifications, they are far less likely to try to sell you an over specified product at an inflated price with higher profit margins.