Motor Oil - Keeping wheels turning

Internal combustion engines, such as those used in cars and motorcycles, contain large numbers of moving parts. The repetitive, high-speed motions of engine components produce heat and friction, which make the engine less efficient at producing power as well as causing damage to its parts. Motor oil, often referred to as the life blood of every car, is designed to cool and lubricate the engine, increasing its efficiency and lifespan by preventing metal surfaces from rubbing against each other and transferring heat away from the surface being lubricated.

  • Types of Motor Oil
  • Synthetic Oils
  • Semi-synthetic Oils
  • Motor Oil Viscosity
  • Mineral Oils
  • Mineral or Synthetic?
  • Bio-based Oils
  • API Service Level Category
  • SAE Viscosity Grades
  • European Standard for car engine oils
  • Choosing the right motor oil for safety
  • Oil drain intervals
  • Conclusion

Choosing the correct motor oil is vital for the proper functioning of any vehicle. Motor oil prevents deposits within the engine and reduces the amount of friction lost in addition to regulating heat and preventing corrosion and rust, all of which is vital to the safe and efficient running of a vehicle. The increase in efficiency of a motor with the use of high-grade motor oil slows the degradation, resulting in an increase in service life. The vehicle manual will often recommend one type of oil over another. The manual may also suggest a viscosity, and sometimes even a specific brand of oil. 

Weather conditions in the area where the vehicle is to be used also have an effect on oil type. In areas where extreme temperature variations are experienced, it may be necessary to use oils of different viscosity for summer and winter. 

Opinion is divided over how much difference the type of oil makes to the lifespan and efficiency of an engine. Some vehicle owners simply buy the cheapest oil available, while others insist on exact specifications, and still others experiment until they find the oil that best suits their needs. Generally speaking, however, a standard vehicle such as a family car can accept a wider range of oils than the more finely tuned engines found in performance and sports vehicles.


Types of Motor Oil

Motor oil products appear under many different brand names and at a wide range of price points. There are specialist and general purpose oils, as well as variants for two stroke and four stroke engines. The main types of motor oil, however, are as follows:

• Mineral oils
• Synthetic oils
• Part synthetic oils
• Bio-based oils

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Synthetic Oils


Synthetic oils are chemical compounds created artificially. In contrast to mineral oils, the chemical structure of synthetics is more uniform, giving them much higher thermal stability. This means that synthetics typically outperform mineral oils at both high (above 185 degrees F) and low (below 0 degrees F) operating temperatures.


Synthetic oils also tend to have a much higher base number retention than petroleum based oils. The base number is a measure of the lubricant’s ability to neutralize acid. A high base number means the lubricant is better able to resist acid, making it useable longer. For this reason, synthetic oils tend to last much longer than other oil types. As a result, oil drain intervals in vehicles that use synthetics tend to be longer than those that do not. Other advantages include higher film strength in some synthetics, a higher viscosity index and lower engine hydrocarbon emissions, among others. On the other hand, this tendency to last longer also means that synthetics are typically more expensive than mineral oils. 

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Semi-synthetic Oils


Part or semi-synthetic oil is a mixture of mineral and synthetic oils, designed to keep costs low while improving the viscosity and lubrication properties of mineral oil. They also provide protection for heavy loads and high temperatures. Blended oils are usually less volatile, meaning the evaporate less, resulting in higher fuel efficiency due to reduced oil loss. These types of oil are usually more expensive than conventional oils, although less expensive than the high-end full synthetic brands.




Motor Oil Viscosity


Viscosity is a liquid’s ability to resist flow. When exposed to heat, motor oil thins. When it cools, it thickens. Generally speaking, motor oil which is more resistant to thinning is considered superior for a car’s engine, as thicker oil tend to be a better sealant and also provides a better and longer-lasting film of lubrication, which helps to protect the car’s moving parts.

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Mineral Oils


Before the development of synthetic oil, most vehicle engines used mineral oil, which is derived from crude oil as a product of the oil distillation process. Because it is simpler to produce than synthetic oil, mineral oil is cheaper, but it may not perform as well across such a wide range of conditions; for example, the presence of wax in mineral oils can lead to poor flow properties in cold weather conditions, and at high temperatures poor oxidation stability can lead to sludge and acid build-up. In addition, the viscosity of mineral oil tends to change significantly with the temperature, resulting in the base oil thinning dramatically at high temperatures.


This is mainly attributed  to the chemical ‘impurity’ of petroleum-based lubricants. Mineral oils are composed of various chemical elements (molecules), each subject to its own evaporation, oxygenation and burn points. Put simply, the moment you start your car, petroleum based oils start changing. Though additives do help to control acid, maintain viscosity levels, and keep soot suspended, these are consumed steadily over time. As a result, car owners using a mineral oil are typically recommended to change their oil every 3,000 to 5,000 miles.


Mineral or Synthetic?


Choosing between mineral and synthetic oils may not be purely a question of budget. A number of factors go into deciding which kind to choose, including the type and age of the vehicle and the local climate. Synthetic or part synthetic oil is recommended for many modern vehicles, especially motorcycles. Conversely, mineral oil tends to be recommended for older engines, since synthetic oil can lead to the breakdown of aging components, and is more likely to transfer contaminants and particles around the system. Synthetic oils are especially well suited for vehicles with high-tech engines such as those that might be found in premium segment vehicles. 

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Bio-based Oils

With increasing concerns about the environmental impact of drilling for fossil fuels, as well as refining and using them, along with the fear that these resources will run out, there has been a great deal of interest in developing biological alternatives to synthetic and mineral motor oils. In the near future, more vehicle engines may be lubricated using vegetable based oils made from grain, seed or nuts. 

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API Service Level Category


This defines whether an oil is suitable for gasoline or diesel engines.

Gasoline engines: The service level category contains two letters. The first letter, S, indicates the oil is for gasoline engines. The codes are as follows:

• SN: For vehicles manufactured after 2010
• SM: Vehicles manufactured between 2002-2009
• SJ: Vehicles manufactured before 2001

Diesel engines: The first letter, C, indicates the oil is for a diesel engine. The codes are:

• CJ-4: Four stroke high speed diesels manufactured from 2010
• CI-4: For vehicles built between 2002 and 2010
• CH-4: Vehicles built between 1998 and 2002

For full details consult the API Motor Oil Guide.

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SAE Viscosity Grades


The SAE viscosity grade for multi-grade motor oils looks like this: SAE 5W-30.

The first number (5W) indicates the cold weather viscosity and the second number (30) is the hot weather viscosity; the lower the number, the thinner the oil.

Vehicle manufacturers specify a range of oil viscosities and the temperature range over which they can be used. It's a very good idea to follow these recommendations, especially for modern engines.

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European Standard for car engine oils


For European vehicles sold in the US, there is a further set of criteria, the ACEA classification. Some oil manufacturers include ACEA classification on their oils in addition to the SAE viscosity classification. Modern engines have very tight tolerances and it's essential that the recommended grade of oil is used, especially with European vehicles. When the correct specification oil cannot be found, it should be purchased directly from the vehicle manufacturers to avoid the possibility of engine failure.


The codes look like this:


A:         petrol engines

B:         diesel engines of cars, light commercial vehicles


A1, B1: standard quality, normal intervals, but: *HTHS-viscosity lowered

A2, B2: standard quality, normal drain intervals

A3, B3: high performance oil, extended intervals are possible

A4:        (reserved for vehicles with petrol direct-injection)

B4:        similar to B3, but also for diesel direct-injection engines

A5, B5: similar to A3 or B4,   but: HTHS-viscosity lowered


The A refers to petrol and the B to diesel engines. Some oil manufacturers include ACEA classification on their oils in addition to the SAE viscosity classification.



C:          petrol and diesel engines with exhaust after treatment


C1:        is suitable for catalytic converter an diesel with particulate filter  (DPF),  low saps & fuel economy, HTHS viscosity is lowered

C2:        is suitable for catalytic converter an diesel with particulate filter (DPF),          mid saps & fuel economy, HTHS viscosity lowered

C3:        is suitable for catalytic converter an diesel with particulate filter (DPF), mid saps

C4:        is suitable for catalytic converter an diesel with particulate filter (DPF), low saps


E:          diesel engines of heavy commercial vehicles


The value stands for different performance categories:


E2:        normal use, normal drain intervals

E3:        heavy use, longer drain intervals possible

E4:        very heavy use, longer drain intervals possible

E5:        similar to E3; also tested for American engines

E6:        similar to E4, yet low ash, suitable for DPF and other exhaust systems

E7:        similar to E5 yet stricter test criteria

E9:        new specification



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Choosing the right motor oil for safety


With regards to safety, the PBT and vPvB values of motor oil are of interest, for these indicate the level of potentially harmful chemicals contained in an oil. Persistent, bio- accumulative and toxic chemicals are classified as PBT, each stating the hazard that they pose to the environment. vPvB is very persistent and very bio-accumulative, so it is worth considering choosing an oil that contains neither PBT nor vPvB substances. The sulphate (ash) content should be between 1-1.5g per 100g, for higher levels lead to a drop in pressure and a reduction in fuel economy, and lower levels would not be able to sufficiently protect the components of an engine and would therefore pose a risk to the driver. The motor oil’s flash point need also be considered, for if an engine reaches high enough temperatures when overheating, then a conversion of fluid to gas should be avoided. A flash point of 446°F (230°C) or slightly below offers a realistic and safe margin, for engines operate at around half this temperature under normal conditions. Taking the flash point as a differentiation between synthetic and regular oils, the 446°F value of synthetic oils is well above that of refined motor oils, thus increasing the preventative measures against the oil igniting. Some regular oils may evaporate/ignite at temperatures of 400°F.

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Oil drain intervals


Every vehicle owner knows that motor oil should be changed regularly to maintain engine health. However, while improvements in engine design mean the intervals between oil changes in modern vehicles are increasing, oil drain intervals are not necessarily uniform across the world. The Automotive Oil Change Association states that, on average, US drivers change their oil roughly every 5,000 miles. This is half the length that most Europeans drive before undertaking an oil change. Not only time-consuming, this puts an additional financial burden on US vehicle owners.

One reason for this difference is the way in which motor oil is ‘controlled’ in these two regions. In Europe, a committee representing automobile manufacturers come together to discuss and finally agree on how to improve on the standards, components and performance of motor oil. In the US, on the other hand, it is the oil manufacturers that make these decisions.

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Motor oil remains vital to keeping vehicle engines running smoothly. Advances in both oil and engine development mean that high quality oils are more affordable, last longer, and perform more effectively. Today's motor oil is available as a synthetic, part synthetic, or mineral formula, with varying viscosity for a wide range of uses and temperatures. Choosing the right oil for the vehicle, and the conditions in which it will be used, topping the oil up when needed, and changing it regularly, helps to prolong the lifespan of the vehicle by maintaining an efficient and economical engine.&nb

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