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Motor oil: Things you can learn from the label

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Manufacturers label the engine oils they produce using codes and numbers that puzzle many car owners. We will try to help you make sense of those!

What properties is motor oil supposed to have?

Motor oil should feature:

  • Solid results at cleaning engine components from insoluble debris.
  • High thermostability and resistance to thermal oxidation.
  • Compatibility with the sealing materials, not aggressive to metal parts.
  • Create a sufficiently thick slippery film for preventing abrasion and wear of the adjacent surfaces. Special additives, for instance, molybdenum disulfide, are often used for this purpose.
  • Retain its original properties for a long time.
  • Optimal viscosity characteristics at any temperature, ensuring efficient lubrication of adjacent surfaces at cold engine start and preventing their wear in hot weather.
  • Resistance to foaming.
  • Low volatility, to minimise environmental pollution.  

Motor oil composition: what are the differences?

Depending on their base stock type and proportions of various additives, engine lubricants are usually divided into 3 types:

  1. Mineral. These are made of fractionally distilled petroleum that  was  further purified with acid or via solvent extraction. They are often labeled as Mineral. These lubricants feature high viscosity levels. When heated, they evaporate quite rapidly and get contaminated due to the chemical breakdown of the additives in their composition.
  2. Semi-synthetic. Based on minerals undergoing special technical processes, these motor oils contain a higher amount of additives as compared to mineral oils. Labeled Semi-synthetic or Part-Synthetic, they work great in areas with mild winters and moderately warm summers. Their cost is lower than that of synthetic oils. They also have a number of advantages over mineral oils, such as longer operation time, higher resistance to temperature changes, and overall efficiency.
  3. Synthetic. Made of oil via organic synthesis. Labeled as Fully Synthetic in most countries. Due to their special formula and cutting-edge technology used in their production, these motor oils prevent sludge deposits from forming and show optimal viscosity characteristics in cold weather conditions, ensuring reliable protection of the engine in the very first seconds after starting. They also retain their original properties even at extremely high temperatures, and are therefore suitable for use in hot climates.

This classification, while being the most common, remains quite superficial and arbitrary, so the American Petroleum Institute (API) specialists split all basic oils into five groups, deliberately avoiding the term “semi-synthetic”.

  1. Group I contains products obtained from oil through solvent extraction and dewaxing.
  2. Group II includes highly purified products with low paraffin and aromatic compound content that underwent hydrocracking.
  3. Group III contains high-viscosity lubricants obtained via catalytic hydrocracking.
  4. Group IV base stock are polyalphaolefins.
  5. Group V features all engine oils not included in any of the abovementioned categories. Their base stocks include esters, glycols, and other substances.

Modern products tend to contain components from several base stock groups.

AutoDoc tip: for older engine models with a large mileage, synthetic oils are contraindicated, especially if mineral oils had been used to lubricate before. First, the additives in these oils can break down the old soot that has already settled and is not really obstructing engine operation; it results in extra load on the power unit, causing wear-out of its components.

Second, synthetic-based products have low viscosity index so they may leak through sealing elements, or even destroy them. However, for sports cars and high-power vehicles, whose units and components undergo extreme strains, mineral oil is inadmissible as the intense thermal impact may break it down.

What does SAE labelling stand for?

Viscosity is one of the essential properties of a motor oil when determining if a specific product can be used in a specific season.

According to the Society of Automobile Engineers (SAE), all motor oils can be divided into the following categories:

  1. Winter. Labeled with a W for winter, these are suitable for cold seasons only. The number preceding the W is always divisible by five and serves to indicate the minimum temperature at which the oil can protect the engine during a cold start. The starting point is -35 °С, equaling grade 0. Each following grade counts up by 5 °С: a 5W product retains its properties at -30 °С, a 10W, at -25 °С, etc.

  2. Summer. These engine oils provide timely lubrication and protection of car parts in warm seasons, but are ineffective in the cold. Their labels also feature numbers: 20, 30, 40, 50 and 60. Contrary to popular belief, these numbers stand for the oil’s kinematic viscosity at 100 °С and not the maximum ambient temperature.

  3. All-season. These are labeled as suitable in the winter, with both minimum temperature and viscosity level at maximum heating temperature: 5W-30, 10W-60, etc. All-season engine oils are currently the most common.

AutoDoc Tip: All-season synthetic oils help save money, since you don't need to change them twice a year. If you mostly drive on urban roads, with frequent stops, and you keep your car in an unheated room, and especially if you live in an area with harsh winters, look for an engine oil labeled as 0W или 5W. However, for a car with a worn engine with enlarged gaps between friction pairs, a higher viscosity product would be preferable.

Making sense of API classification

The American Petroleum Institute developed their own classification meant to sort engine oils based on their formula and operation properties. It also allows to indirectly evaluate the quality of lubricants since lately, the standards have become much more stringent as compared to earlier years of the industry.

According to API, all motor oils fall into two categories, each containing several classes:

S. For petrol engines. In most countries, the following four classes are currently approved for use:

  • SJ. Recommended for use in engines manufactured before 2001.
  • SL. Suitable for power units produced before 2004. A lot of car manufacturers have adopted SL as the minimum standard required for car maintenance.
  • SM. Intended for engines produced in 2010 and earlier. SM oils are highly efficient at low temperatures, resistant to oxidation and sediment formation. They retain their excellent properties throughout their service life.
  • SN. Introduced in 2010. Currently, these are the oils that can ensure the highest level of engine protection, as well as its high efficiency. SN oils help save fuel. They prevent the turbocharger from wearing out prematurely, without aggressive effects on seals and gaskets.

C. Designation for engine oils for diesel-fueled commercial vehicles. The classes currently in use for vehicles of different model years are CH, CI, CJ, and CK. The number 4 following the class designation stands for 4-stroke engine vehicles. Let’s look at C-grade oils  in detail:

  • CH-4. Introduced in 1998. Suitable for engines that run on high-quality fuel ranging in sulfur content up to 0.5% weight.
  • CI-4. Introduced in 2002. This type of motor oils ensures reliable protection of the engine and exhaust system from soot deposits and prevent premature wear-out of their elements. Some lubrication materials of this class are designated CI-4 PLUS.
  • CJ-4. They boast elevated temperature stability, resistance to oxidation and longer service life.
  • CK. Developed for protection of engines that were produced in 2017. However, such motor oils can be used optionally in earlier engine models.

There are universal lubricants available, suitable for use in both petrol and diesel engines. They have double designations, for instance, CН-4/SJ.

AutoDoc Tip: A lot of the manufacturers recommend to use the latest-class oil for engine lubrication. And in most cases, this advice is justified: the more recent the formula, the safer, as well as more economical and environmentally friendly it is. However, this recommendation is useless for older vehicles since their engines are built differently, and will not be able to get the maximum out of all the advantages of a pricier oil. You can find more information on which lubrication to use in your car in your service book.

АСЕА performance evaluation

Decreasing emission toxicity and reducing fuel consumption are one of the crucial requirements for modern lubricating materials. Hence lots of oils would indicate they meet the latest ecology standards on their package.

According to the Association des Constructeurs Européens d'Automobiles ( ACEA ) classification, all engine oils approved for sale and use can be divided into the following categories:

  • А. For petrol engines. This category includes three classes: А1, А3 and А5. The letter precedes a number indicating eco-safety level and viscosity under specific conditions. The numbers 1 and 5 indicate fuel economy, but otherwise it's just like API: the higher the number, the better properties a product has.
  • В. This category includes lubricants for passenger and small commercial vehicles running on diesel fuel. They are also divided into classes: B1 and B5 mean fuel economy, while В3 and В4 are regular products.
  • Е. Oils marked with this letter are intended for diesel-fueled heavy-duty lorries and special vehicles. E1 stands for fuel economy; the rest are standard.

Fuel economy was a parameter that API specialists also decided to take into account, introducing a new designation, EC (Energy Conserving).

These oils boast lower viscosity at extreme temperature rises, ensuring smooth and even travel of moving parts and cutting fuel consumption. However, this means a thinner lubricating film, which is especially risky for older engines with a big mileage – those engines need additional protection.

Does the manufacturer's endorsement really matter?

A product may work great for some engines while posing a risk for others. This compels vehicle manufacturers to do their own lubricant performance tests. If a product passes a test successfully, it will get marked accordingly, for example, BMW Longlife-98. This means an oil can be used in vehicles of this brand with longer maintenance intervals, manufactured in 1998 and later.

AutoDoc tip: Always try to use the oil recommended by your car manufacturer, and do not experiment with viscosity levels. The risks lies in the fact that in some engines, the lubrication grooves are only thick enough for high-viscosity oils. If disregarded, the power unit will inevitably wear out prematurely. At the same time, some car manufacturers, e.g. BMW Group and Daimler AG, bly advise against using low-viscosity lubricants in their vehicles, due to the design of their engines.

What do different engine oil classifications have in common?

Despite their differing principles, all classifications are closely related. For instance, if a lubricant is API-marked as SH, it can't be an А1 or А5 in ACEA, since those requirements were not published until SJ class came out. If a label features А5, it means the products is at least an SL in API, i.e., it has longer change intervals.

Fuel economy products labeled as А1, А5, В1 и В5 tend to have temperature viscosity of 30 and less. Oils with viscosity of 40 belong to А2, А3, В2, В3, and В4 classes and do not provide fuel economy.

Learning to read labels

API SL / CF. This stands for a universal oil suitable for both multivalve turbocharged petrol-run engines and diesel power trains of various designs. The product provides increased protection for engines running on lean fuel-air mix and prevents carbon deposits from forming when using fuel with ash content over 0,5 %.

ACEA A3 / B4. This indicates that the lubricant is suitable for use in heavy-duty conditions, helps reduce fuel consumption and is to be replaced less often. May be used in high-performance petrol and diesel engines.

10W-40. The oil is suitable for both winter and summer seasons, retains its viscosity at -25 °С and remains quite viscous when heated, meaning it can be used in vehicles with a big mileage.

MoS2. The molybdenum disulfide in the formula of this oil prevents galling, reduces friction and wear out of the components, provides noiseless engine operation.

Teilsynthetisches Leichtlauf-motorenöl. This means that the oil is semi-synthetic.

To resume: When choosing engine lubricating products, one should follow the vehicle manufacturer's recommendations and not the cost or popularity of a specific oil brand. Make sure to calculate the road conditions, your own driving style, and other individual factors into the equation: that's the only surefire way of picking the right lubricant. Stay safe from counterfeits by following our tips and shopping at AutoDoc!

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