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Making Sense of Engine Oil: The Basics

Updated: Jun 27, 2019




Engine oil is often regarded as the lifeblood of the engine - it plays a critical role in the engine by reducing friction and heat, thereby ensuring peak performance while prolonging the life of components. In this article, we'll give you a brief overview of what engine oils do and what to look out for when choosing the oil for your next oil change. With the mind-boggling selection of engine oils available on the shelves, it can be hard to tell which oil to use and why you might choose one over the other. Fear not, we're here to help break it down for you. First up, what do engine oils really do? The primary and most obvious function of engine oil is to reduce friction, thus making movement of components smoother and more efficient while cutting down the wear on these moving parts - it achieves this function by not only forming a lubricating layer, but also by cleaning the engine of sludge and other undesirable contaminants within the engine with the help of additives. The engine oil also works to improve the seal between piston rings and cylinder wall and by acting as a coolant in its own right to carry heat away from moving components. Additives such as corrosion inhibitors further maintain the engine's health particular where the external elements such as moisture are concerned. The conditions within which the engine oil must perform these vital functions are quite extreme - heat, pressure and contaminants all push engine oils to their limits. Poor maintenance practices and lower quality lubricants quickly and almost inevitably cause the engine to wear itself out or, in the most extreme cases, fail catastrophically. Indeed, without engine oil, not only would the engine essentially be grinding itself to destruction, but most engines would almost inevitably succumb the the elements as corrosion and contamination would set in. A healthy and effective engine oil provides the benefits such as:

  • Optimum engine output

  • Optimum fuel efficiency

  • Heat management

  • Optimal engine wear and component service life

  • Emissions control

  • Cold weather/Low-Temperature startup

With this in mind, it's easy to see why engine oil is so important, but what makes an engine oil good and how does one tell the difference between engine oil and snake oil? Read on to find out more. First up, let's give a brief overview of the two broad categories of oil-based lubricants that exist: 1) Mineral Oil - Consist of less highly refined base oils; these are used for a wide range of applications because they are cheap and easy to produce and generally meet the standards required for simple and less demanding application such as sewing machines and lubricating chopping boards; special applications such as engine break-in also require the use of specific type of mineral oils such as break-in oil - such oils make use of the specific properties of mineral oils, in combination with certain additives in order to help with seating piston rings.


2) Synthetic Oils - Made from highly refined stock of base oils, these have more impurities removed and as a result, the molecules in these oils are more consistent. Due to the more consistent nature of the molecular arrangement, the molecules are better able to assist in the lubricating function. This aside, their purity allows synthetic oils to perform well across a wider range of temperatures and conditions - they have better low temperature viscosity, and high temperature stability. Additionally, because they have less impurities, the formation of deposits is also much decreased, thus making them better for the engine health in the longer run.

Additives - one plus one? To further enhance the performance, longevity and other benefits of the engine oil, manufacturers often blend additives into the lubricant. You may have heard of engine oils which claim to reduce deposits or clean then engine as they work - well, this effect is achieved through the use of additives. Generally as each manufacturer adds their own cocktail of additives based on research, testing and so on, the result is an engine oil that (in theory) should perform better in one way or another compared to lubricants without additives Beyond that, there are also additives that may be inserted separately into the engine oil as well - these include friction reducers and detergents marketed at further enhancing engine oils. While it's not within the scope of this article to test and come to any definitive conclusion on the topic of additives - in general, most additives tend to be redundant to modern premium synthetics because the manufacturers have often already added similar additives to the blend of engine oils and adding anything beyond that might actually upset the balance of of the engine oil (ratio of base oil to additives) and cause other potential issues. As a result, unless the supplier has definitive support or warranties on the product, such additives may not be a good idea. Beyond that, the cost of additives tends to make them counter-intuitive to claims such as being "cost-saving" or "fuel-efficiency-improving" because the additives themselves bear a cost to purchase - something which may or may not be offset by the savings in petrol consumption and the like. Always do your research before adding anything to your engine oil - the same logic applies to fuel and other fluid elements because such claims tend to be hard to substantiate and your every vehicle is, in reality a unique case - what works for your vehicle may not work for others and vice versa. Since test scenarios reflect controlled environments, the results may not reflect the reality of your use case. While both mineral oils and synthetic oils may include additives, in general, the more consistent nature of synthetics means that the chemical composition and properties of the oil mean that the effect of the additives is more predictable and stable - something which is highly desirable when it comes to the world of lubricants. How regularly should you be changing your engine oil. In order to understand how regularly you should be changing your engine oil, let's briefly detail what happens if you don't change your engine oil frequently enough. So you know how all the good things that the engine oil is supposed to do for the engine, but what about when engine oil gets bad? For starters (pun not intended), putting off oil changes can lead to damage particularly during cold starts - this is the time that the engine wear is the typically the greatest. Oil that is left in service too long eventually breaks down and turns into sludge which not only does a lousy job of lubricating the vital elements of the rotating assembly (bearings, rods, pistons etc.) but also has to function as a conduit for carrying heat away as it is generated by the engine during movement. During cold starts when the lubricant is at its lowest circulation - a healthy fluid protects the engine from wear by remaining as a lubricating film so that less stress and wear is placed on the components as the engine is cranked. Beyond just starting the car, when engine oil has deteriorated to the point where it starts to form sludge, it can and will clog the oiling system, journals and so on which may require the complete replacement of the engine itself. Numbers, number, numbers. Now that we have an understanding of the general differences between the types of engine oils, let's take a look at what all those numbers accompanying engine oil names mean. The first and most important consideration when determining the suitability of an engine oil to the task is the oil's resistance to flow - i.e. the viscosity or weight. These are indicated by the grade in the SAE Vicosity Index which is typically found on the front of the package - e.g. 0W-40 and so on. The oil grade can be single (in which case the grade is indicated as SAE xx) or multi-grade (with formats such as xWxx - such as the earlier example of 0W-40 or 0W40 - the dash is academic). Single grade oils, as their name implies, only have a single grade to indicate their viscosity under operation at temperature. multi-grade oils, on the other hand, feature two different viscosity indicators - the first rating with the suffix "W" indicates the viscosity during cold operation - the lower the number the less viscous it is, meaning that is flows more easily. The second rating indicates the viscosity at high temperatures - as with the cold operation rating, the lower the number the less viscous it is. Aside from the SAE Vicosity Index, the ACEA European standard also serves to provide another indicator of the suitability of a lubricant for a specified task - the ACEA represents the 15 mos important European vehicle manufacturers and sets standards that lubricant makers benchmark and set their products to match. Let's take a look at the engine oil label below for a quick rundown to make sense of these numbers:

A Handy Guide On How To Read the EO Label - as illustrated with the Castrol Edge 5W-40

In the example above, the "Viscosity" as per the SAE standards is indicated as 5W-40, which means that the this is a dual-grade engine oil with a "winter"/cold operation viscosity of '5' and a warm/hot operation viscosity of 40. The "A/B" category for the ACEA Classification indicates that this is an "A3/B4" lubricant which is "stable, stay-in-graded engine oil for passenger cars & light duty petrol and direct injection diesel engines". A note on viscosity and how it relates to temperature: As the oil warms up during operation, it becomes thinner which means that although it flows more smoothly, it may become thin to the extent where part on part contact occurs. However, you also don't want to be using an oil which is too viscous as it requires more effort to move through, thereby reducing the efficiency of the engine. As such, it's important to consider the operating conditions and use cases when choosing an engine oil - it indeed a very fine balance. What oil should you be using for your ride? How often should you be changing your engine oil? Provided your vehicle's engine has not had extensive modifications (by which we mean changes to engine components, pistons, forced induction and so on), it's a safe bet to follow the manufacturer's guidelines on the oil grades to use and the recommended servicing internals - generally around 5000km and above. With the advent of modern synthetics lubricants and improved component durability, these intervals have been growing longer steadily. Where the information from the manufacturer may not be available, or where local climatic conditions may fall out of the regular scope, a simple rule of the thumb is to picking which grade to use is to consider the ambient temperature. Here's a very simple chart to help you figure out which oil grade to use based on the ambient temperature of your vehicle's operating environment.

Recommended Engine Oil: Ambient Temperature vs Viscosity Grades
graphic: DriveSense Pte Ltd

What else to look out for?

In addition to servicing regularly and keeping up with oil changes, it's still a good practice to monitor the health of the engine oil. The contaminants within the engine oil serve as an important indicator of the health of the engine and early detection can mean the difference between a simple change of one or two parts or an expensive complete overhaul. Taking a look at the debris in the oil pan and filter can be very revealing. Indeed, it's not uncommon to see debris containing bits of aluminum, silicone, iron/steel, or carbon or more. The quantity and grain of such elements can tell serve as a guide to help investigate what is happening inside the engine. In this regard the engine oil has a very useful, if under-appreciated extra function. Indeed, while it is possible to send your engine oil or filters to laboratories for analysis, often, the contents of the debris are obvious enough that most competent owners and workshops will be able to analyze it and begin investigation. Aside from the debris collected in filters and oil pans, low oil-levels can also serve as an indicator that all is not well within the engine - typically worn seals, piston rings or leaks can cause oil levels to drop below healthy levels, a situation that can cause major damage if left unchecked. Changes in the smell of the engine oil also serve as indicators that there might be something going wrong somewhere within the engine - typically when lubrication is incomplete or not taking place properly, for example, the engine oil can even develop a "burning smell" after some time as whatever oil that is in the engine is overworked and cooked as a result. With this general overview, we hopefully you'll have a greater appreciation and understanding of engine oil. Indeed, understanding the fluids in your car is often the best first step to really understanding how the car works and how to maintain it. If you've enjoyed this article, please feel free to drop us a like on facebook and share the article with friends or family who you think might be interested!


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