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Engine Oil Types and Grades Explained: Viscosity and Thickness Charts

Table of content

Oil grades and viscosity explained
What does the SAE oil labelling stand for? The meaning of the numbers
1. Motor oil viscosity chart
Types of engine oil
Motor oil: properties and specifications
АСЕА performance evaluation
Do the manufacturer's classifications and testing really matter?
What do different engine oil classifications have in common?

Motor oil is the magic substance that lubricates, cleans, and cools your engine, ensuring smooth operation and longevity. The numbers on oil packaging, such as 10W-30, represent its viscosity (thickness) and performance in different temperatures. This blog breaks down the different oil types and grades, explaining what these numbers mean and how to choose the right oil for your vehicle.

Oil grades and viscosity explained

The oil viscosity grade is arguably the most important out of all the oil specifications. It determines how easily the oil flows through the system under different conditions and the level of protection provided. These grades are determined by the Society of Automotive Engineers (SAE) and can usually be found on the front of the oil bottle.

What does the SAE oil labelling stand for? The meaning of the numbers

The SAE oil labelling shows a set of numbers which indicate the lubricant’s cold viscosity and hot viscosity grades, e.g. “10W-40”. In this example, the 10W represents the oil’s cold (“winter”) rating, indicating how well it flows in cold conditions. The lower this number is, the more fluid it is and the easier it flows in low temperatures, facilitating cold starts.

The hot viscosity is the number that comes after the winter rating (on multi-grade oil), which in this case is “40”. A higher viscosity grade means that the lubricant film will be thicker in high temperature conditions, ensuring that the metal parts stay protected.

On the downside, using an oil that is too thick for your car engine will place unnecessary stress on the parts and increase wear and fuel consumption. If it is too thin, however, it may not provide enough protection.

Motor oil viscosity chart

Below, you’ll see a chart showing the common oil viscosity ratings from thinnest to thickest.

Chart showing the common oil viscosity ratings

Types of engine oil

The main types include conventional, fully synthetic, semi-synthetic, and high-mileage oils. Each type is designed for specific vehicle operating requirements. Understanding these differences helps ensure optimal engine performance, longevity, and protection in varying conditions.

Mineral: These products are made of fractionally distilled petroleum that has been purified further with acid or through solvent extraction. These lubricants have high viscosity levels. When heated, they degrade quite quickly and get contaminated due to the chemical breakdown of the additives in their composition.
Semi-synthetic: Based on a blend of mineral and chemically engineered synthetic oils, these lubricants contain a higher amount of additives compared to mineral oils. They work great in areas with mild winters and moderately warm summers. They usually cost less than synthetic oils. They also have a number of advantages over mineral oils, such as longer service life, higher resistance to temperature changes, and overall efficiency.
Synthetic: Made through a process of organic synthesis. Labelled as fully synthetic in most countries. Due to their special formulas and the cutting-edge technology used in their production, these motor oils prevent sludge deposits from forming and offer optimal viscosity characteristics in cold weather conditions. This ensures reliable engine protection during 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.

BMW Quality Longlife-04 5011987001831 Engine oil 5W-30, 1l

BMW Engine oil 5W-30, 1l

Article number: 5011987001831

compared to RRP £ 28,67

£ 27,00

£ 27,00 for 1 litre

price incl. 20% VAT, excl. delivery costs

MANNOL ENERGY MN7511-10 Engine oil 5W-30, 10l, Part Synthetic Oil

MANNOL Engine oil 5W-30, 10l, Part Synthetic Oil

Article number: MN7511-10

compared to RRP £ 34,30

£ 25,05

£ 2,51 for 1 litre

price incl. 20% VAT, excl. delivery costs

VAG LONGLIFE III FE GS55545M2 Engine oil 0W-30, 1l

VAG Engine oil 0W-30, 1l

Article number: GS55545M2

£ 37,71

£ 37,71 for 1 litre

price incl. 20% VAT, excl. delivery costs

BMW TwinPower Turbo 83212365929 Engine oil 0W-30, 1l

BMW Engine oil 0W-30, 1l

Article number: 83212365929

£ 24,20

£ 24,20 for 1 litre

price incl. 20% VAT, excl. delivery costs

MANNOL Traktor Superoil MN7406-10 Engine oil 15W-40, 10l, Mineral Oil

MANNOL Engine oil 15W-40, 10l, Mineral Oil

Article number: MN7406-10

£ 38,19

£ 3,82 for 1 litre

price incl. 20% VAT, excl. delivery costs

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”.

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

Modern products tend to contain compounds from several base groups.

AUTODOC tip: for older engine models with a high mileage, using synthetic oils is counterproductive, especially if mineral oils had been used to lubricate the vehicle before. First of all, it could cause the seals to shrink, resulting in leaks. In addition, the additives may disrupt the sludge buildups from the mineral oil, causing blockages.

In contrast, for sports cars and high-power vehicles whose units and components undergo extreme pressures and temperatures, mineral oil is not suitable as the harsh conditions may break it down.

Motor oil: properties and specifications

Motor oil should offer the following:

Solid results when cleaning insoluble debris off engine components
High thermostability and resistance to thermal oxidation
Compatibility with the seal materials, not harsh on metal parts
Creates a sufficiently thick slippery film to prevent abrasion and wear on contact surfaces. Special additives, such as molybdenum disulfide, are often used for this purpose
Retains its lubricating properties for a long time
Optimal viscosity characteristics at any temperature, ensuring efficient lubrication of surfaces during cold engine starts and preventing wear in hot weather
Resistance to foaming
Low volatility, to minimise environmental pollution

Making sense of API classifications: the API grades and their differences

The American Petroleum Institute (API) developed its own classifications to sort engine oils based on their formulas and operating properties. It also allows manufacturers to evaluate the quality of lubricants as the standards have become much more stringent compared to previous years.

Energy API

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. Designed for diesel engines. 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 don’t have advanced after-treatment systems and have a sulphur content of up to 0.5% wt.
CI-4. Introduced in 2002. This type of motor oil ensures reliable protection of the engine and exhaust system from soot deposits and prevents premature wear. Some lubricants in this class are designated CI-4 PLUS.
CJ-4. These lubricants boast elevated temperature stability, resistance to oxidation, and a longer service life.
CK. Developed to protect engines that were produced in 2017 onwards. However, these motor oils have voluntarily been used by some manufacturers in some earlier engine models.

There are also lubricants that are suitable for use in both petrol and diesel engines. They have double classifications, e.g. CН-4/SJ.

AUTODOC Tip: Only use the exact oil type recommended by the vehicle manufacturer to ensure proper lubrication and compliance with standards. It is not a good idea to use more advanced oils in a very old engine that has not been designed for this.

MOTUL 800 FL OFF ROAD 2T 104039 Engine oil 4l

MOTUL Engine oil 4l

Article number: 104039

£ 65,84

£ 16,46 for 1 litre

price incl. 20% VAT, excl. delivery costs

TOYOTA Fuel Economy 08880-80845 Engine oil 5W-30, 5l

TOYOTA Engine oil 5W-30, 5l

Article number: 08880-80845

£ 45,17

£ 9,03 for 1 litre

price incl. 20% VAT, excl. delivery costs

LIQUI MOLY Top Tec 4200 3707 Engine oil 5W-30, 5l

LIQUI MOLY Engine oil 5W-30, 5l

Article number: 3707

£ 57,22

Price per item

£ 11,44 for 1 litre

price incl. 20% VAT, excl. delivery costs

MANNOL ContiClassic MN7501-10 Engine oil 10W-40, 10l, Part Synthetic Oil

MANNOL Engine oil 10W-40, 10l, Part Synthetic Oil

Article number: MN7501-10

compared to RRP £ 32,53

£ 23,88

£ 2,39 for 1 litre

price incl. 20% VAT, excl. delivery costs

MANNOL LONGLIFE 504/507 MN7715-10 Engine oil 5W-30, 10l

MANNOL Engine oil 5W-30, 10l

Article number: MN7715-10

compared to RRP £ 41,34

£ 31,55

£ 3,16 for 1 litre

price incl. 20% VAT, excl. delivery costs

АСЕА performance evaluation

Decreasing emission toxicity and reducing fuel consumption are one of the crucial requirements for modern lubricants. This is why many brands specify that their products meet the latest environmental standards on their packaging.

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

Association des Constructeurs Européens d'Automobiles

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. Designed 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 more advanced 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 according to their viscosity and performance: B1, B3, B4 and B5.
Е. Oils marked with this letter are intended for diesel-fueled, heavy-duty lorries and special vehicles.

Do the manufacturer's classifications and testing 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: Do not experiment by using different viscosity levels to the ones in the car manual. In some engines, the oil grooves are not thick enough for high-viscosity products. If disregarded, the power unit will inevitably wear out prematurely. At the same time, some car manufacturers 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 ACEA А1 or А5 since those requirements were not published until the SJ class was introduced. If a label is marked А5, it means the product has an API rating of at least SL, i.e. it has longer change intervals.

Fuel economy products labelled А1, А5, В1 or В5 tend to have a viscosity rating of 30 or less. Oils with viscosity rating of 40 belong to the А2, А3, В2, В3, and В4 categories and are not necessarily fuel-saving.

Learning to read oil labels and numbers

Engine oil specifications

API SL / CF. This indicates it is a universal oil suitable for both multi-valve turbocharged petrol-run engines and diesel powertrains of various designs. The product provides increased protection for engines running on a lean fuel-air mix and prevents carbon deposits from forming when using fuel with an ash content of over 0.5 %.

ACEA A3 / B4. This indicates that the lubricant is suitable for use in high-demand applications, helps reduce fuel consumption, and is changed less frequently. 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 sufficiently thick when heated, meaning it can be used in vehicles with a high mileage.

MoS2. The molybdenum disulfide in the formula of this oil prevents galling, reduces friction and wear, and promotes silent engine operation.

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

To conclude, when choosing engine oils, you should always follow the vehicle manufacturer's recommendations and not make decisions purely based on the cost or popularity of a specific oil product. Make sure to consider the road conditions, your own driving style, and other individual factors.

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