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Knowledge Centre / FAQ


1.) Why motor oil?

Motor Oil is an oil used for lubrication of various internal combustion engines. These include motor or road vehicles such as cars and motorcycles, heavier vehicles such as buses and commercial vehicles, non-road vehicles such as go-karts, snowmobiles, boats (fixed engine installations and outboards), lawn mowers, large agricultural and construction equipment, locomotives and aircraft, and static engines such as electrical generators.

In engines, there are parts which move against each other causing friction which wastes otherwise useful power by converting the energy to heat. Contact between moving surfaces also wears away those parts, which could lead to lower efficiency and degradation of the motor. This increases fuel consumption and decreases power output and can, in extreme cases, lead to engine failure. By lubricating the contact areas, motor oil can prevent these problems to a high extent.

Motor oil has to operate under extreme pressure and temperatures: In petrol (gasoline) engines, the top piston ring can expose the motor oil to temperatures of 160 °C (320 °F). In diesel engines the top ring can expose the oil to temperatures over 315 °C (600 °F).

2.) What are the functions of motor oil?

As described above the main function is to lubricate moving parts by creating a separating film between surfaces of adjacent moving parts to minimize direct contact between them, reducing wear and decreasing heat caused by friction and thus protecting the engine. It also improves sealing.

But additionally motor oil cools the engine by carrying heat away from moving parts: In use, motor oil transfers heat through convection by means of air flow over the surface of the oil pan, an oil cooler and through the build-up of gases (that are then evacuated by the Positive Crankcase Ventilation (PVC) system). Furthermore motor oil cleans the engine by carrying away the by-products of combustion. Which is why it is completely normal for the oil to turn black after a short while in your engine – it simply means that it does its job! Coating metal parts with oil also keeps them from being exposed to oxygen, inhibiting oxidation at elevated operating temperatures and thus preventing rust or corrosion.

So-called chemical additives like corrosion inhibitors may also be added to the motor oil. Many motor oils also have detergents and dispersants added to help keep the engine clean and minimize oil sludge build-up (mostly by keeping the by-products in suspension).

Modern high-tech engines usually require a set of very specific motor oil qualities that can be met with almost tailor-made ‘cocktails’ of base oils and additives and lead to all those different SAE-grades, API- and ACEA-specifications as well as OEM-approvals of motor oils.

3.) What do you need an oil filter for?

Although motor oil reduceswear considerably, the rubbing of metal engine parts will inevitably produce some microscopic metallic particles from the wearing of the surfaces. Such particles could circulate in the oil and grind against moving parts, causing additional wear. Because particles accumulate in the oil, it is typically circulated through an oil filter to remove harmful particles. An oil pump, a vane or gear pump powered by the engine, pumps the oil throughout the engine, including the oil filter.

4.) Which motor oil is the right one for my car?

As mentioned above, modern high-tech engines usually require a set of very specific motor oil qualities that can be met with almost tailor-made ‘cocktails’ of base oils and additives and lead to all those different grades and specifications that you can find on the bottles.

As the choice of the right motor oil is of utmost importance for the engine, the OEMs (original equipment manufacturers) give detailed instructions in the car manual on which motor oils to use, including SAE-grade and ACEA/API-specification. Stick to it! Otherwise you do not only run the risk of seriously damaging your engine, but you’ll also lose the warranty the manufacturers give on it.

Additionally to the API/ACEA-specifications, many European car manufacturers issue their own “OEM-approvals” that often go beyond the API/ACEA-specifications. If that is the case, you’ll find the code of the required approval in the car manual. The oils that carry these approvals (e.g. VW 505 00, Mercedes-Benz 229.3, BMW Longlife-04) have been additionally tested and approved by the manufacturers themselves as fitting for their engine. Once again we recommend you to stick to it in order not to lose the warranty on your engine!

5.) How often should I change the motor oil?

Oil is the life-blood of an engine: Regular oil changes are one of the most important things that can be done to help extend the life of an engine! Each OEM (original equipment manufacturer) tests his own vehicle in combination with the recommended motor oils in order to determine the proper drain interval. Therefore please check the vehicle owner’s manual: It does not only specify the exact type of motor oil to be used, but also the related recommended oil change intervals. But generally speaking synthetic motor oils will allow longer drain intervals, and severe driving conditions will demand shorter drain intervals.

6.) What are severe driving conditions?

Severe use typically includes frequent stop-and-go driving, short trips and high-speed-driving. But also external conditions such as dust, high engine load and unusually high or low ambient temperatures mean higher stress for the motor oil. However once again we recommend you to first check your manual to see what the manufacturer has to say about that: Often they give clear instructions regarding driving habits and related recommended oil draining intervals.

7.) Why and how should I check the oil level?

The oil fill should strictly move between the minimum and the maximum level prescribed by the manufacturer (following the marks on the dipstick). And even though modern engines hardly consume any motor oil anymore, we still strongly advise to check the oil approximately every 1.000km. Too big are the possible damages, e.g. piston jamming, should there be not enough motor oil in the oil-circulation system. But also overfill can cause serious damage both to engine and catalytic converter, so don’t pour more oil into the engine than the allowed maximum! If you feel the need to run additional oil for additional protection, e.g. for racing, install a larger oil pan. But that’s another story.

In order to check the oil level in your car, park the car at level plain and wait for about 5-10 min. after the engine has stopped. This allows the oil in the system (usually 200-500ml) to flow back into the oil pan and thus a more precise measurement. Pull out the dipstick and wipe it clean from the spillage occurred during driving, before inserting it again and pulling it out carefully once more and reading the level on the dipstick. If the oil level is below the minimum you have to fill it up. (Just as a rough hint: In passenger cars the difference between the min. and max. level is usually about 1l). But be careful to proceed slowly and to recheck the level in between in order to avoid overfilling! If by accident you clearly went beyond the maximum level, we strongly advise you to drain some oil. As annoying as that might be, it is worth the trouble as you avoid bigger and expensive damage.

8.) What exactly is motor oil made of?

The basic formula is: Base Oils + Additives = Motor Oil

Base oils can consist either of petroleum-based and/or of synthesized (non-petroleum) chemical compounds. They are responsible for the basic lubricating quality of motor oil that can be further enhanced by diverse additives (see below). The American Petroleum Institute (API) has defined 5 base oil categories:

Group I 
Mineral base oils (by fractional distillation of petroleum plus solvent extraction), containing < 90% saturates and/or > 0.03% sulfur and a viscosity index (VI) of 80 VI < 120.
Group II/II+ Mineral base oils (by fractional distillation of petroleum plus hydro cracking), containing ≥ 90% saturates and ≤ 0.03% sulfur and a viscosity index (VI) of 80 ≤ VI < 120
Group III Highest level of mineral base oils (further hydro cracking of Group II base oils or hydroisomerization of slack wax), containing ≥ 90% saturates and ≤ 0.03% sulfur and a viscosity index (VI) ≥ 120. Though highly refined they are still mineral base stocks and are considered synthetic motor oil ONLY in the United States; in the rest of the world they count as the mineral part of semi-synthetic lubricants.
Group IV Synthetic Polyalphaolefins (PAO)
Group V Synthetic esters and other non-PAO synthetics (including diesters, polyolesters, alkylated napthlenes, alkyklated benzenes, etc.)

Synthetic base stocks are man-made (synthesized) from compounds other than petroleum and are tailored to have a controlled molecular structure with predictable properties, unlike mineral base oils which are complex mixtures of naturally occurring hydrocarbons.

Additives:They are chemical components designed to improve specific characteristics of motor oil. They comprise 'viscosity index improvers', detergents and dispersants to help keep the engine clean by minimizing sludge build-up, corrosion inhibitors and alkaline additives to neutralize acidic oxidation products of the oil. Most commercial oils have a minimal amount of zinc dialkyldithiophosphate as an anti-wear additive to protect contacting metal surfaces with zinc and other compounds in case of metal to metal contact. The quantity of zinc dialkyldithiophosphate however is limited to minimize adverse effect on catalytic converters. Another aspect for after-treatment devices is the deposition of oil ash, which increases the exhaust back pressure and reduces over time the fuel economy. Therefore many manufacturers today limit the allowed concentrations of sulfur, ash and phosphorus in motor oils (low-SAPs). Additionally you can find various other extreme-pressure additives and antiwear additives for motor oil.

9.) Viscosity, viscosity index and the related SAE-Grade (e.g. 10W-40)

Viscosity: One of the most important properties of motor oil in maintaining a lubricating film between moving parts is its viscosity. The viscosity of a liquid can be thought of as its "thickness" or a measure of its internal resistance to flow. Water for example is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity.

The viscosity of motor oil must be high enough to maintain a lubricating film, but low enough that the oil can flow around the engine parts under all conditions. The viscosity index (VI) is a measure of how much the oil's viscosity changes as temperature changes. A higher viscosity index indicates the viscosity changes less with temperature than a lower viscosity index. Thus motor oils with higher viscosity indices thin less at these higher temperatures, ensuring a constant oil film.

SAE-Grade: The kinematic viscosity of motor oil is graded by measuring the time it takes for a standard amount of oil to flow through a standard orifice, at standard temperatures. The longer it takes, the higher the viscosity and thus higher the so-called SAE code: The Society of Automotive Engineers (SAE) has established a numerical code system for grading motor oils according to their viscosity characteristics.

SAE viscosity gradings include the following, from low to high viscosity: 0, 5, 10, 15, 20, 25, 30, 40, 50 or 60. The numbers 0, 5, 10, 15 and 25 are suffixed with the letter W, designating their "winter" (not "weight") or cold-start viscosity, at lower temperature. The number 20 comes with or without a W, depending on whether it is being used to denote a cold or hot viscosity grade.

Note that the SAE has a separate viscosity rating system for gear, axle, and manual transmission oils, which should not be confused with engine oil viscosity. The higher numbers of a gear oil (e.g. 75W-140) do not mean that it has higher viscosity than an engine oil.

Single-grade Oils (e.g. SAE 30): For some applications, when the temperature ranges in use are not very wide, single-grade motor oil is satisfactory; for example, lawn mower engines, industrial applications, and vintage or classic cars.

Winter-grades: Based on the coldest temperature the oil passes at, that oil is graded as SAE viscosity grade 0W, 5W, 10W, 15W, 20W, or 25W. The lower the viscosity grade, the lower the temperature the oil can pass.
on-winter grade oils: Here the kinematic viscosity is measured at a temperature of 100 °C (212 °F). Based on the viscosity of the oil at that temperature, the oil is graded as SAE viscosity grade 20, 30, 40, 50, or 60. In addition, for SAE grades 20, 30, and 40, a minimum viscosity measured at 150 °C (302 °F) and at a high-shear rate is also required.

Multi-grade Oils (e.g. 10W-40): The temperature range the oil is exposed to in most vehicles however is too wide for single-grade oils, ranging from cold temperatures in the winter when the vehicle is started up to hot operating temperatures in summer weather. That’s where multi-grade oils come in:

By nature the oil will have a high viscosity when cold and a lower viscosity at the engine's operating temperature. The problem here is that during cold-starts the thick oil needs longer to get to the necessary engine parts and do its job, whereas at higher operating temperatures it might get too thin and the coating film could break in some places.

To bring the difference in viscosities closer together, special polymer additives called viscosity index improvers (VIIs) are added to the oil. These additives are used to make the oil a multi-grade motor oil (e.g. 10W-40). The idea is to cause the multi-grade oil to have the viscosity of the base grade when cold and the viscosity of the second grade when hot. This enables one type of oil to be generally used all year. In fact, when multi-grades were initially developed, they were frequently described as “all-season oil”.

10.) API- / ACEA- / JASO- Specifications and OEM-Approvals

All these organizations are setting standards for lubricants, prescribing minimum performances in standardized tests for each of their categories. This classification of motor oils allows the user to discern which motor oil will fit his engine and its specific needs, as each service manual will contain a recommendation for motor oil based on at least one of those 4 systems. Engine oil which has been tested and meets the respective standard may display the corresponding code and/or symbol on the label.

API-specifications: The American Petroleum Institute has established two general classifications: S for "service" (originating from spark ignition, for typical passenger cars and light trucks using gasoline engines), and C for "commercial" (originating from compression ignition, for typical diesel equipment). Current categories include SM, SL and SJ for gasoline engines and CJ-4, CI-4, CH-4, CG-4, CF-2, and CF for diesel engines. In addition, API created a separated CI-4 PLUS designation in conjunction with CJ-4 and CI-4 for oils that meet certain extra requirements.
It is possible for an oil to conform to both the gasoline and diesel standards.

ACEA-specifications are defined by the European Automobile Manufacturers Association. Their categories are A/B (gasoline and diesel engine oils: A1/B1, A3/B3, A3/B4, A5/B5), C (catalyst compatibility oils: C1, C2, C3, C4) and E (heavy duty diesel engine oils: E2, E4, E6, E7). The performance/quality classifications A3/A5 tests used in Europe for example are arguably more stringent than the API standards.

JASO-specifications: The Japanese Automotive Standards Organization (JASO) has created their own set of performance and quality standards for petrol engines of Japanese origin. Typical codes are MA, MA-2, MB, FA, FB, FC etc.

OEM-approvals: By the early 1990s, many of the European original equipment manufacturer (OEM) carmakers felt that the direction of the American API oil standards was not compatible with the needs of a motor oil to be used in their motors. As a result many leading European motor manufacturers created and developed their own "OEM" oil standards.

Probably the most well known of these are the VW50*.0* series from Volkswagen Group, and the MB22*.** from Mercedes-Benz. Other European OEM standards are from General Motors, for the Vauxhall, Opel and Saab brands, the Ford "WSS" standards, BMW Special Oils and BMW Longlife standards, Porsche, and the PSA Group of Peugeot and Citroën.

Because of the real or perceived need for motor oils with unique qualities, many modern European cars will demand a specific OEM-only oil standard. As a result, they may make no reference at all to API standards, nor SAE viscosity grades. They may also make no primary reference to the ACEA standards, with the exception of being able to use a "lesser" ACEA grade oil for "emergency top-up", though this usually has strict limits, often up to a maximum of ½ a liter of non-OEM oil.

11.) How can I judge the quality of motor oil?

Quality counts! Above mentioned standards of renowned organizations (e.g. API, ACEA, JASO, OEMs, ISO, DIN) assure and reflect a strictly defined quality level for motor oils: For each code specific test have to be passed before getting the authorization to carry the code on the bottle, e.g. A3/B4, E7 (ACEA), VW 505.00 (OEM), GL-5 (API). Hence those codes ensure the quality of an oil more reliably and independently than commercials or big names.

As a rule of a thumb fully synthetic oils offer the highest quality, followed by semi-synthetics and then conventional mineral oils.

12.) What is the difference between mineral oils, semi-synthetic and synthetic oils?

The 3 categories differ regarding the type of base oil(s) that is being used for their production. The choice of base stock alone strongly influences the resulting characteristics of the motor oil. The additive package does the rest, but doesn’t have any saying in the categorization of the motor oil.

Mineral oils are the “traditional” motor oils, based on mineral base oils (Group I, II/II+, III) only. They are widely used in combination with additive packages and ensure a basic protection for the engine. Typical SAE-grades for mineral oils are 10W-40, 15W-40 or mono-grades like SAE30.

Semi-synthetic oils are blends of mineral base oils (Group I, II/II+, III) with no more than 30% synthetic oils (Group IV and/or V), plus the additive package. They are designed to have many of the benefits of synthetic oil without matching the cost of pure synthetic oil. As a rule over thumb you might say their properties lie in the middle of mineral and fully-synthetic oils. Typical grades are 5W-30, 10W-40.

Synthetic oils are exclusively made of synthetic stock, i.e. Group IV and/or Group V base oils. Because of their tailor-made structure and purer composition they generally offer superior mechanical and chemical properties than those found in traditional mineral oils. Typical grades are 0W-30, 5W-30, 0W-40 or racing oils. Their main advantages are:

  • Measurably better low and high temperature viscosity performance
  • Better chemical & shear stability
  • Decreased evaporative loss
  • Resistance to oxidation, thermal breakdown and oil sludge problems
  • Extended drain intervals with the environmental benefit of less oil waste.
  • Improved fuel economy in certain engine configurations.
  • Better lubrication on cold starts
  • Longer engine life

13.) Switching from mineral oil to synthetic oil

Most experts and motor oil producers state clearly that nowadays it is no problem for cars of any age to switch from mineral oils to synthetic oils and back – always providing that you stick to the motor oils and specifications (e.g. SAE- and ACEA-code) that are endorsed in your car’s manual. Technical progress has dealt with the former occasional problem of leaking gaskets and seals in the process.

If you drive a really old car however, you might want to have a closer look at the question. We recommend Chris Longhurst's article “If I put new, fully synthetic oil in my older engine, will the seals leak?”. It offers a thorough and perspicuous evaluation on the issue.

14.) Should I use aftermarket additives?

Since most motor oils nowadays already contain their own package of additives (especially multigrade oils), we disadvise you to use additional aftermarket additives: Additives are chemical compounds that can react with each other. You can be pretty sure that the additives in your motor oil are selected in a way NOT to react with each other in an undesired way, but you cannot be sure what will happen when you add another additives cocktail to the existing one.






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