Engine Lubrication Explained

Even allowing for the fact that automotive lubricants have come a long way in the last few decades, they are not created equal, particularly in the off-road context, where the demands and operating conditions of off-road driving and vehicles are such that only the best lubricants will do. However, almost all manufacturers of lubricants claim their products are better formulated; more extensively tested, used by more racing and competition teams than any other because it is best at cleaning engines, and to top it all, they have won every conceivable prize and award in the recent past.

Advertising hype apart, a quick glance at the list of specifications and formulations on any oil or grease container is enough to leave anyone confused. What do the acronyms API, MilSpec, or SAE stand for, and are they important? Well, yes but not all of them: there are literally hundreds of abbreviations and acronyms used in the lubrication industry, but for the purposes of lubricating a 4×4 vehicle, only a few are really important. However, what is more important is knowing what is in the oil, aka, the FORMULATION, which depends on the purpose of the oil and the type of engine it is to used in and is of critical importance, especially if you need to source oil in the middle of the equatorial rain forests of Africa. So, what makes up the oil in the typical 4×4 engine?

Engine Oil Formulation

Engine oil is much more than just refined crude oil: up to 20% of any given volume of engine oil consists of additives, collectively known as the PAP, or Performance Additive Package and include detergents, dispersants, friction modifiers, antioxidants, foaming and corrosion inhibitors, antifriction agents, and viscosity improvers. So, what does all this mean?

• Dispersants:

These are additives that prevent sludge formation by keeping contaminants in suspension until they are removed at the next service. Not all contaminants are removed via the oil filter, which makes regular oil changes an absolute requirement.


High temperature areas like the rings and surrounds, and the underside of the piston crown are particularly susceptible to the formation of carbon deposits, which the detergent component in the oil prevents.

Anti-Wear Agents:

By itself, oil does not provide sufficient protection in high load and temperature areas like the camshafts, valve lifters, rings, and cylinder walls. Thus, anti-wear agents in the oil create a layer, sometimes called a “sacrificial film”, between metal surfaces to prevent metal-to-metal contact. This film is consumed, or worn away, as the oil ages, another fact that makes regular oil changes necessary to increase engine life.

• Friction Modifiers:

As the name suggests, these additives are added to increase oil’s limited lubricating ability under all and any conditions. Generally speaking, they help to maintain maximum efficiency and reduce fuel consumption. However, these additives lose much of their effectiveness as oil ages.


Contact with oxygen hastens the thickening of oil at high temperature; with the formation of sludge and other deposits a distinct possibility as the oil ages. Antioxidants assist in the slowing of the oxidation process in oil, thus preventing the formation of sludge and carbon deposits.

• Anti-Foam Additives:

A secondary function of oil is to assist in the cooling of the engine, and air bubbles, that often result from over filling the engine with oil, seriously reduces oil’s ability to carry away heat from the underside of the pistons and cylinder head. Foaming oil is also much harder to effectively move around the engine, with the result that engine components may not receive adequate lubrication. The addition of anti-foaming agents generally reduces oil’s ability to foam, particularly in very high temperature conditions.

• Rust and Corrosion Inhibitors:

Water vapour sucked into the engine as it cools down can cause serious rust and corrosion deposits inside an engine, but by coating internal surfaces as the oil splashes about, this potentially serious problem is largely prevented.

• Viscosity Index Improvers:

Viscosity refers to a liquid’s resistance to flow, and since cold oil does not flow as easily as when it is hot, effective lubrication in very cold weather can be problematic. The addition of certain polymers as additives helps to iron out the large differences in the flow rates of oil under varying temperatures, thus making it possible to produce oil with relatively stable flow characteristics. One example is the popular multi-grade oil, SAE 10W-30.

Connecting the Dots…

Now that the formulation of oils is a little clearer, how do the acronyms such as SAE, ANSI, or OEM figure into all of this? Here is where knowing what a few acronyms stand for, since not all oils have all of the above additives, or any at all. In recent years, thriving businesses in many parts of the developing world, South Africa included, involving the collection of discarded engine oil from workshops have sprung up like toad stools.

Old engine oil containing anything from water, brake fluid, automatic transmission fluid, cigarette butts, gear oils, antifreeze and much else besides is collected, mechanically filtered, and resold to auto parts shops, and even some repair shops in mostly unsealed containers at ridiculously low prices. Cutting open these containers will almost invariably reveal a deposit of sludge, water, and sometimes, even metal fragments. The only protection against this practice is the price: if it is too cheap, and/or the container is not sealed, don’t buy it!

However, reputable manufacturers seal their containers and print on their labels the names of the professional bodies that have tested and recommended their products for general use. Space precludes the listing of all testing authorities and/or acronyms but the ones most likely to be found on oil containers in Africa are:

• SAE: (The Society of Automotive Engineers) (SAE): An engineering association dedicated to the development, collection, and dissemination of knowledge of automobile technology. The designation “SAE” on motor oils signifies that an oil product complies with the standards of the society. Link: www.sae.org
• ACEA: (Association of the European Automobile Manufacturers) Link: www.acea.be
• AGMA: (American Gear Manufacturers Association) Link: www.agma.org
• API: (The American Petroleum Institute) Link: www.api.org
• API Gear Lubricant Service Designation: – (Refers to the classifications and designations pertaining to lubricating oils suitable for automotive transmissions developed by API in conjunction with SAE and ASTM.)
• API Engine Service Classification System: Refers to the classifications and designations for lubricating oils for automotive engines developed by API in conjunction with SAE and ASTM.)
• ASEAN: (Association of South-East Asian Nations) Link: http://www.asean.org/
• ASTM: (The American Society for Testing and Materials (ASTM) is a professional society that is responsible for the publication of test methods and the development of test evaluation techniques.) Link: www.astm.org

In the off-road context, adequate engine lubrication is of cardinal importance: it is just not good enough to use the cheapest oil on the premise or assumption that all oils are the same on the one hand, and that oil never loses its lubricity, on the other. Nothing could be further from the truth and keeping in mind the old adage that, “Knowledge is power”, more information on oils and additives for automotive use can be found at; http://www.synlube.com/glossary.htm

And Understanding the Numbers

Most people have only a vague idea what the various terms and numbers on oil containers signify: some denote viscosity, other refer to grades, while still others refer to formulations and/or specifications. What does it all mean, and do the numbers make any difference? To anybody who is not a chemical engineer these numbers can be extremely confusing, however, they are not all important to the uninitiated: some are of academic interest only, but to the layman who needs to fill the engine of an off-road vehicle with the best possible lubricant, some are more important than others, particularly those relating to grade and specification.

• Multigrade:

Multigrade refers to oil’s ability to flow at acceptable rates at both low and high temperatures, thus oil labelled as SAE (Society of American Engineers)10w-40, merely means that it is able to flow at a specific rate at a low temperature. The “w” in the designation means “winter”, and the lower the first number is, the colder the temperature at which the oil can be used. To measure this, a standardized test orifice is used through which the oil must flow at a specific rate.

The higher number refers to the rate of flow through a test orifice while at a temperature of 100°C. This temperature is a fixed limit and all oils that end with a 30, 40, or 50 must achieve their respective flow rates at this temperature. To clarify, oil ending with “30”, is lighter and will flow through the test orifice at a higher rate than both oils ending in a “40” or “50”.

• Specification:

There are a great many oil specifications in the market today, with almost all manufacturers of cars insisting on their own, specific formulations. However, the truth is that almost all oils can be used in all vehicle engines, with the clear exception that petrol oil must not be used in diesel engines and vice versa.

The main criterion should only be that an API (American Petroleum Institute) certification should appear on the label or container. These oils (petrol and diesel) comply with the standards and specifications of all major carmakers, which are fond of touting the latest automotive or other engine technologies as being present only on their vehicles, when the truth is that automotive developments are for the most part driven by environmental concerns and most developments in emission control measures soon find their way to all manufacturers. There is therefore no oil meant for only one, specific make of car to the exclusion of all others.

While it is true that vehicles built before the early 1970’s used oil, which when used in modern engines, can destroy a modern engine in very short order, the modern oils available today can be used in just about any modern engine with no adverse effects. While a car user manual may specify a particular brand of oil, the use of any other brand having the same rating and specification can be substituted with no negative effects.

However, it should be borne in mind that certain oils are prescribed for a reason; if a manufacturer specifies the use of fully synthetic oil for instance, do not substitute this oil for anything else. These engines are subject to extremely high stresses and strains and oil with a designation that is “almost the same”, will not only cause the destruction of the engine, it will also cause the repudiation of warranty claims.

Petrol vs. Diesel Oil

• Viscosity:

The single biggest (and most crucial) difference lies in the relative viscosity of the two oils. The higher viscosity of diesel oil could cause insufficient lubrication at low temperatures in petrol engines. Another problem is that once the oil does get pumped around the engine, the increased flow friction could increase engine (and oil) temperatures to the point where the oil breaks down, and loses its lubricity. Generally speaking, for every 10 deg C in temperature, the effectiveness of oil is reduced by 50%.

• Catalytic converter damage:

While the basic formulation of petrol and diesel oils are largely the same, diesel oils contain much higher concentrations of anti-wear agents in the form of ZDDP, or more precisely, Zinc Dialkyl Dithiophosphate, because of the higher pressures between wear surfaces in diesel engines. Catalytic converters in diesel exhaust systems are able to handle this added load while the catalytic converters in petrol exhaust systems are not.

• Cylinder wall wear:

Diesel oil also contains higher concentrations of detergents due to the fact that diesel engines produce more combustion by-products than petrol engines. The extra detergents in diesel oil will thus do what it is supposed to; clean the oil film off the cylinder walls in petrol engines. Additionally, the sudden change to diesel oil could clean off all the sludge and carbon deposits from the internal surfaces of a petrol engine which could conceivably cause serious, and possibly fatal blockages in small diameter oil galleries and passages.

Identification of engine oil

All oils licensed by the API (American Petroleum Institute), carry an identification mark in the form of a doughnut on the container or label. This symbol will clearly indicate either an “S”, meaning the oil is suitable for use in spark ignited (petrol engines), or a “C”, indicating that the oil is meant for use in compression ignited (diesel) engines.

Synthetic vs. mineral oils

• Mineral oil:

Mineral oil is refined crude oil and is made by distilling the crude oil in a fractionating tower, a process during which the usable fractions of the crude oil is collected at different points and temperatures along the height of the tower. The fractions most suitable for the making of engine oil is collected, filtered, and mixed with additives. This is a relatively simple process; however, the demands of modern engines, environmental concerns, and market conditions have led to the formulation of very complicated formulations. Nevertheless, he demands of modern engines have to some degree outpaced the developments of mineral oils and the inherent disadvantages, or shortcomings of mineral oil have made the development of synthetic oils necessary.
The single biggest drawback of mineral oil, despite the addition of viscosity modifiers, is the fact that it cannot maintain a single flow rate at all temperatures, which is a major consideration in the 4×4 context, where engines frequently work at relatively low RPM’s. While oil pressure in these conditions is generally not affected, the volume of oil delivered by the pump most certainly is. High engine speeds equate to higher volumes of oil pumped around the engine, which in turn means that the more oil there is at any given point the better it is lubricated.

• Synthetic oil:

While mineral oil shave reached a very high state of development, it has not yet become possible to remove all hydrocarbon-based contaminants from the final product. For instance, refined mineral oils contain varying amounts of different waxes that contribute nothing to the lubricity of the base oil.
Synthetic oil on the other hand, does not contain any of these contaminants since it is not made by distilling crude oil: instead, it is made by the Fischer-Tropsch process, using raw materials such as methane, carbon monoxide, and carbon dioxide. Contrary to popular belief, synthetic oil is not new: it was first developed in Germany during WW 2, when that country experienced an acute shortage of crude oil stocks.

  • The single biggest advantage of synthetic oil is that it has vastly superior flow properties over mineral oils, even at temperatures where mineral oil will not flow at all. Some formulations of synthetic oils flow as much as seven times easier and faster than mineral oils.
  • Another advantage is the fact that synthetic oil does not need to be changed as often as mineral oils, due to the fact that heat and oxidation do not affect synthetic oil to the same extent as mineral oil. This means that synthetic oil maintains its lubricity for longer, while at the same time remaining cleaner for longer.
  • While synthetic oil contains hydrocarbons in the form of methane, and is thus not strictly synthetic in the sense that it contains no organic compounds, it does contain little or no contaminants such as sulphur and waxes that cause the formation of sludge and various varnishes.

However, while synthetic oil is generally considered to be superior to mineral oil in most respects, there are some disadvantages to this oil:

  • It is expensive:
    Some formulations and brands can be up to three times as expensive as comparable mineral oils, but this must be balanced against the fact that oil changes can be less frequent, but more importantly, that the increased lubricity of synthetic oil, especially on turbo-equipped engines, equates to significantly longer component life.
  • Oil changes are still required:
    Even with the improvements in lubricity, synthetic oil still “wears out”, and has to be replaced from time to time, albeit at longer intervals.
  • It does not eliminate engine wear:
    Using synthetic oil may extend engine life; however, there is no lubricant in existence that can completely eliminate engine wear.

How does lubrication work?

Even the smoothest machined surface found in the engine of any 4WD vehicle is not perfectly so- machining and polishing procedures leave behind microscopic valleys and ridges, called asperities. These peaks cause friction when they come into contact with one another, however, the valleys act as minute oil reservoirs, and since the oil film between wear surfaces is thicker than the peaks are high, direct contact between the peaks is avoided and where contact does occur, the additives in the contained in the valleys provides lubrication.

Wear occurs because the peaks are gradually worn down through momentary direct contact where they pierce the protective layer, increasing the clearance between surfaces. In the case of worn crankshaft bearing inserts for instance, the clearance eventually becomes too great for the oil film to absorb the shock at the top and bottom of the stroke with the result that the protective oil film is squeezed out. Wear patterns in other components generally follow the same route. Contaminated oil or oil in which the anti-wear additives have degraded, effectively hastens the wear process, by not being able to prevent direct contact between wear surfaces.

So, although mineral and synthetic oils can be mixed in any ratio, and some mixed formulations are on sale, it must be borne in mind that the best properties of each can only be taken advantage of if each is used on its own. For instance, while adding synthetic oil to mineral oil may enhance the lubricity of the mix, the presence of mineral oil in the mix detracts from the proven advantages of pure synthetic oil. However, given the demands of off-road conditions, any real, substantial gains in the lubricity of engine oil are advantageous.