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Lubricant used for lubrication of internal combustion engines

Motor oil, engine oil, or engine lubricant is any one of various substances used for the lubrication of internal combustion engines. They typically consist of base oils enhanced with various additives, particularly antiwear additives, detergents, dispersants, and, for multi grade oils, viscosity index improvers. The main function of motor oil is to reduce friction and wear on moving parts and to clean the engine from sludge (one of the functions of dispersants) and varnish (detergents). It also neutralizes acids that originate from fuel and from oxidation of the lubricant (detergents), improves the sealing of piston rings, and cools the engine by carrying heat away from moving parts. In addition to the aforementioned basic constituents, almost all lubricating oils contain corrosion and oxidation inhibitors. Motor oil may be composed of only a lubricant base stock in the case of non detergent oil, or a lubricant base stock plus additives to improve the oil's detergency, extreme pressure performance, and ability to inhibit corrosion of engine parts. Motor oils are blended using base oils composed of petroleum based hydrocarbons, polyalphaolefins (PAO), or their mixtures in various proportions, sometimes with up to 20% by weight of esters for better dissolution of additives.

On 6 September 1866, American John Ellis founded the Continuous Oil Refining Company. While studying the possible healing powers of crude oil, Dr. Ellis was disappointed to find no real medicinal value, but was intrigued by its potential lubricating properties. He eventually abandoned the medical practice to devote his time to the development of an all petroleum, high viscosity lubricant for steam engines – which at the time were using inefficient combinations of petroleum and animal and vegetable fats. He made his breakthrough when he developed an oil that worked effectively at high temperatures. This meant fewer gummed up valves and corroded cylinders.

Motor oil is a lubricant used in internal combustion engines, which power cars, motorcycles, lawnmowers, engine generators, and many other machines. In engines, there are parts which move against each other, and the friction between the parts wastes otherwise useful power by converting kinetic energy into heat. It also wears away those parts, which could lead to lower efficiency and degradation of the engine. Proper lubrication decreases fuel consumption, decreases wasted power, and increases engine longevity. Lubricating oil creates a separating film between surfaces of adjacent moving parts to minimize direct contact between them, decreasing frictional heat and reducing wear, thus protecting the engine. In use, motor oil transfers heat through conduction as it flows through the engine. In an engine with a recirculating oil pump, this heat is transferred by means of airflow over the exterior surface of the oil pan, airflow through an oil cooler, and through oil gases evacuated by the positive crankcase ventilation (PCV) system. While modern recirculating pumps are typically provided in passenger cars and other engines of similar or larger in size, total loss oiling is a design option that remains popular in small and miniature engines. 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 (599 °F). Motor oils with higher viscosity indices thin less at these higher temperatures. Coating metal parts with oil also keeps them from being exposed to oxygen, inhibiting oxidation at elevated operating temperatures preventing rust or corrosion. 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. The oil is able to trap soot from combustion in itself, rather than leaving it deposited on the internal surfaces. It is a combination of this and some singeing that turns used oil black after some running. Rubbing of metal engine parts inevitably produces some microscopic metallic particles from the wearing of the surfaces. Such particles could circulate in the oil and grind against moving parts, causing 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. Oil filters can be a full flow or bypass type. In the crankcase of a vehicle engine, motor oil lubricates rotating or sliding surfaces between the crankshaft journal bearings (main bearings and big end bearings) and rods connecting the pistons to the crankshaft. The oil collects in an oil pan, or sump, at the bottom of the crankcase. In some small engines such as lawn mower engines, dippers on the bottoms of connecting rods dip into the oil at the bottom and splash it around the crankcase as needed to lubricate parts inside. In modern vehicle engines, the oil pump takes oil from the oil pan and sends it through the oil filter into oil galleries, from which the oil lubricates the main bearings holding the crankshaft up at the main journals and camshaft bearings operating the valves. In typical modern vehicles, oil pressure fed from the oil galleries to the main bearings enters holes in the main journals of the crankshaft. From these holes in the main journals, the oil moves through passageways inside the crankshaft to exit holes in the rod journals to lubricate the rod bearings and connecting rods. Some simpler designs relied on these rapidly moving parts to splash and lubricate the contacting surfaces between the piston rings and interior surfaces of the cylinders. However, in modern designs, there are also passageways through the rods which carry oil from the rod bearings to the rod piston connections and lubricate the contacting surfaces between the piston rings and interior surfaces of the cylinders. This oil film also serves as a seal between the piston rings and cylinder walls to separate the combustion chamber in the cylinder head from the crankcase. The oil then drips back down into the oil pan. Motor oil may also serve as a cooling agent. In some engines oil is sprayed through a nozzle inside the crankcase onto the piston to provide cooling of specific parts that undergo high temperature strain. On the other hand, the thermal capacity of the oil pool has to be filled, i. e. the oil has to reach its designed temperature range before it can protect the engine under high load. This typically takes longer than heating the main cooling agentwater or mixtures thereofup to its operating temperature. In order to inform the driver about the oil temperature, some older and most high performance or racing engines feature an oil thermometer. Continued operation of an internal combustion engine without adequate engine oil can cause damage to the engine, first by wear and tear, and in extreme cases by "engine seizure" where the lack of lubrication and cooling causes the engine to cease operation suddenly. Engine seizure can cause extensive damage to the engine mechanisms.

An example is lubricating oil for four stroke or four cycle internal combustion engines such as those used in portable electricity generators and "walk behind" lawn mowers. Another example is two stroke oil for lubrication of two stroke or two cycle internal combustion engines found in snow blowers, chain saws, model airplanes, gasoline powered gardening equipment like hedge trimmers, leaf blowers and soil cultivators. Often, these motors are not exposed to as wide of service temperature ranges as in vehicles, so these oils may be single viscosity oils. In small two stroke engines, the oil may be pre mixed with the gasoline or fuel, often in a rich gasoline:oil ratio of 25:1, 40:1 or 50:1, and burned in use along with the gasoline. Larger two stroke engines used in boats and motorcycles may have a more economical oil injection system rather than oil pre mixed into the gasoline. The oil injection system is not used on small engines used in applications like snowblowers and trolling motors as the oil injection system is too expensive for small engines and would take up too much room on the equipment. The oil properties will vary according to the individual needs of these devices. Non smoking two stroke oils are composed of esters or polyglycols. Environmental legislation for leisure marine applications, especially in Europe, encouraged the use of ester based two cycle oil.

The Society of Automotive Engineers (SAE) has established a numerical code system for grading motor oils according to their viscosity characteristics known as SAEJ300. This standard is commonly used throughout the world, and standards organizations that do so include API and ACEA. The grades include single grades, such as SAE 30, and also multi grades such as SAE 15W 30. A multi grade consists of a winter grade specifying the viscosity at cold temperatures and a non winter grade specifying the viscosity at operating temperatures. An engine oil using a polymeric viscosity index improver (VII) must be classified as multi grade. Breakdown of VIIs under shear is a concern in motorcycle applications, where the transmission may share lubricating oil with the motor. For this reason, motorcycle specific oil is sometimes recommended. The necessity of higher priced motorcycle specific oil has also been challenged by at least one consumer organization.

The oil and the oil filter need to be periodically replaced; the process is called an oil change. While there is an entire industry surrounding regular oil changes and maintenance, an oil change is a relatively simple car maintenance operation that many car owners can do themselves. It involves draining the oil from the engine into a drip pan, replacing the filter, and adding fresh oil. In engines, there is some exposure of the oil to products of internal combustion, and microscopic coke particles from black soot accumulate in the oil during operation. Also, the rubbing of metal engine parts produces some microscopic metallic particles from the wearing of the surfaces. Such particles could circulate in the oil and grind against the part surfaces causing wear. The oil filter removes many of the particles and sludge, but eventually, the oil filter can become clogged, if used for extremely long periods. The motor oil and especially the additives also undergo thermal and mechanical degradation, which reduces the viscosity and reserve alkalinity of the oil. At reduced viscosity, the oil is not as capable of lubricating the engine, thus increasing wear and the chance of overheating. Reserve alkalinity is the ability of the oil to resist the formation of acids. Should the reserve alkalinity decline to zero, those acids form and corrode the engine. Some engine manufacturers specify which Society of Automotive Engineers (SAE) viscosity grade of oil should be used, but different viscosity motor oil may perform better based on the operating environment. Many manufacturers have varying requirements and have designations for motor oil they require to be used. This is driven by the EPA requirement that the same viscosity grade of oil used in the MPG test must be recommended to the customer. This exclusive recommendation led to the elimination of informative charts depicting climate temperature range along with several corresponding oil viscosity grades being suggested. In general, unless specified by the manufacturer, thicker oils are not necessarily better than thinner oils; heavy oils tend to stick longer to parts between two moving surfaces, and this degrades the oil faster than a lighter oil that flows better, allowing fresh oil in its place sooner. Cold weather has a thickening effect on conventional oil, and this is one reason thinner oils are manufacturer recommended in places with cold winters. Motor oil changes are usually scheduled based on the time in service or the distance that the vehicle has traveled. These are rough indications of the real factors that control when an oil change is appropriate, which include how long the oil has been run at elevated temperatures, how many heating cycles the engine has been through, and how hard the engine has worked. The vehicle distance is intended to estimate the time at high temperature, while the time in service is supposed to correlate with the number of vehicle trips and capture the number of heating cycles. Oil does not degrade significantly just sitting in a cold engine. On the other hand, if a car is driven just for very short distances, the oil will not fully heat up, and it will accumulate contaminants such as water, due to lack of sufficient heat to boil off the water. Oil in this condition, just sitting in an engine, can cause problems. Also important is the quality of the oil used, especially with synthetics (synthetics are more stable than conventional oils). Some manufacturers address this (for example, BMW and VW with their respective long life standards), while others do not. Time based intervals account for the short trip drivers who drive short distances, which build up more contaminants. Manufacturers advise to not exceed their time or distance driven interval for a motor oil change. Many modern cars now list somewhat higher intervals for changing oil and filter, with the constraint of "severe" service requiring more frequent changes with less than ideal driving. This applies to short trips of under , where the oil does not get to full operating temperature long enough to boil off condensation, excess fuel, and other contamination that leads to "sludge", "varnish", "acids", or other deposits. Many manufacturers have engine computer calculations to estimate the oil's condition based on the factors which degrade it, such as RPM, temperature, and trip length; one system adds an optical sensor for determining the clarity of the oil in the engine. These systems are commonly known as s or OLMs. Some quick oil change shops recommend intervals of , or every three months; this is not necessary, according to many automobile manufacturers. This has led to a campaign by the California EPA against the "3,000 mile myth", promoting vehicle manufacturer's recommendations for oil change intervals over those of the oil change industry. The engine user can, in replacing the oil, adjust the viscosity for the ambient temperature change, thicker for summer heat and thinner for the winter cold. Lower viscosity oils are common in newer vehicles. By the mid 1980s, recommended viscosities had moved down to 5W 30, primarily to improve fuel efficiency. A typical modern application would be Honda motor's use of 5W 20 (and in their newest vehicles, 0W 20) viscosity oil for Engine designs are evolving to allow the use of even lower viscosity oils without the risk of excessive metal to metal abrasion, principally in the cam and valve mechanism areas. In line with car manufacturers push towards these lower viscosities in search of better fuel economy, on 2 April 2013 the Society of Automotive Engineers (SAE) introduced an SAE 16 viscosity rating, a break from its traditional "divisible by 10" numbering system for its high temperature viscosity ratings that spanned from low viscosity SAE 20 to high viscosity SAE 60.

The API oil classification structure has eliminated specific support for wet clutch motorcycle applications in their descriptors, and API SJ and newer oils are referred to be specific to automobile and light truck use. Accordingly, motorcycle oils are subject to their own unique standards. See JASO below. As discussed above, motorcycle oils commonly still use the obsolescent SF/SG standard.

The International Lubricant Standardization and Approval Committee (ILSAC) also has standards for motor oil. Introduced in 2004, GF 4 applies to SAE 0W 20, 5W 20, 0W 30, 5W 30, and 10W 30 viscosity grade oils. In general, ILSAC works with API in creating the newest gasoline oil specification, with ILSAC adding an extra requirement of fuel economy testing to their specification. For GF 4, a Sequence VIB Fuel Economy Test (ASTM D6837) is required that is not required in API service category SM. A key new test for GF 4, which is also required for API SM, is the Sequence IIIG, which involves running a , GM 3.8 L V 6 at , 3,600 rpm, and 150 °C (302 °F) oil temperature for 100 hours. These are much more severe conditions than any API specified oil was designed for: cars which typically push their oil temperature consistently above 100 °C (212 °F) are most turbocharged engines, along with most engines of European or Japanese origin, particularly small capacity, high power output. The IIIG test is about 50% more difficult than the previous IIIF test, used in GF 3 and API SL oils. Engine oils bearing the API starburst symbol since 2005 are ILSAC GF 4 compliant. took effect in October 2010. The industry had one year to convert their oils to GF 5 and in September 2011, ILSAC no longer offered licensing for GF 4. After nearly a decade of GF 5, ILSAC released final GF 6 specifications in 2019, with licensed sales to oil manufacturers and re branders to begin 1 May 2020. There are two GF6 standards; GF 6A being a progression and fully backwards compatible with GF 5, and GF 6B specifically for SAE 0W 16 viscosity oil.

The ACEA (Association des Constructeurs Européens d'Automobiles) performance/quality classifications A3/A5 tests used in Europe are arguably more stringent than the API and ILSAC standards. CEC (The Co ordinating European Council) is the development body for fuel and lubricant testing in Europe and beyond, setting the standards via their European Industry groups; ACEA, ATIEL, ATC and CONCAWE. ACEA does not certify oils, nor license, nor register, compliance certificates. Oil manufacturers are themselves responsible for carrying out all oil testing and evaluation according to recognised engine lubricant industry standards and practices. Popular categories include A3/B3 and A3/B4 which are defined as "Stable, stay in grade Engine Oil intended for use in Passenger Car & Light Duty Van Gasoline& Diesel Engines with extended drain intervals" A3/B5 is suitable only for engines designed to use low viscosities. Category C oils are designated for use with catalysts and particulate filters while Category E is for heavy duty diesel.

The Japanese Automotive Standards Organization (JASO) has created their own set of performance and quality standards for petrol engines of Japanese origin. For four stroke gasoline engines, the JASO T904 standard is used, and is particularly relevant to motorcycle engines. The JASO T904 MA and MA2 standards are designed to distinguish oils that are approved for wet clutch use, with MA2 lubricants delivering higher friction performance. The JASO T904 MB standard denotes oils not suitable for wet clutch use, and are therefore used in scooters equipped with continuously variable transmissions. The addition of friction modifiers to JASO MB oils can contribute to greater fuel economy in these applications. For two stroke gasoline engines, the JASO M345 (FA, FB, FC, FD) standard is used, and this refers particularly to low ash, lubricity, detergency, low smoke and exhaust blocking. These standards, especially JASO MA (for motorcycles) and JASO FC, are designed to address oil requirement issues not addressed by the API service categories. One element of the JASO MA standard is a friction test designed to determine suitability for wet clutch usage. An oil that meets JASO MA is considered appropriate for wet clutch operations. Oils marketed as motorcycle specific will carry the JASO MA label.

A 1989 American Society for Testing and Materials (ASTM) report stated that its 12 year effort to come up with a new high temperature, high shear (HTHS) standard was not successful. Referring to SAE J300, the basis for current grading standards, the report stated:
The rapid growth of non Newtonian multigraded oils has rendered kinematic viscosity as a nearly useless parameter for characterising "real" viscosity in critical zones of an engine There are those who are disappointed that the twelve year effort has not resulted in a redefinition of the SAE J300 Engine Oil Viscosity Classification document so as to express high temperature viscosity of the various grades In the view of this writer, this redefinition did not occur because the automotive lubricant market knows of no field failures unambiguously attributable to insufficient HTHS oil viscosity.

Some current engine or vehicle manufacturers require a specific oil formula, known as oil specs, be used to add extra levels of protection for special engine designs, materials and operating conditions. Starting in the late 1990's BMW for example came out with a spec called LL 98 (Long Life 1998) which requires special additives in oils that were approved to meet that spec. BMW regularly develops new specs to meet the increasing demands of the EPA emission standards and MPG requirements as well as new engines. Failure to use the correct specification oil has been known to cause PCV (positive crankcase ventilation), VVT (variable valve timing) system, gasket and sealing system, and other internal combustion component premature clogging and other failures. Some of the additives in those specs are designed to aid in keeping systems lubricated and clean. Some examples of BMW's other specs are: LL 01,LL 01 fe, LL 12, LL 14+, LL 17 fe. European vehicle manufacturers have led the way for oil specs but Asian and American manufacturers have since joined in creating a need for oil change, repair shops and dealerships to carry many different oils to avoid damages both mechanical and monetarily. Examples of some VW specs are VW 500.00, VW 501.01, VW 502.00, VW 503.00, VW 503.01, VW 504.00, VW 505.00, VW 505.01, VW 506.00, VW 507.00, VW 508.00/509.00. Mercedes Benz specs include MB 226.5, MB 226.51, MB 229.1, MB 229.31, MB 229.5, MB 229.51, MB 229.52.

In addition to the viscosity index improvers, motor oil manufacturers often include other additives such as detergents and dispersants to help keep the engine clean by minimizing sludge buildup, 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 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 fuel economy over time. The so called "chemical box" limits today the concentrations of sulfur, ash and phosphorus (SAP). There are other additives available commercially which can be added to the oil by the user for purported additional benefit. Some of these additives include:
Antiwear additives, like zinc dialkyldithiophosphate (ZDDP) and its alternatives due to phosphorus limits in some specifications. Calcium sulfonates additives are also added to protect motor oil from oxidative breakdown and to prevent the formation of sludge and varnish deposits. Both were the main basis of additive packages used by lubricant manufacturers up until the 1990s when the need for ashless additives arose. Main advantage was very low price and wide availability (sulfonates were originally waste byproducts). Currently there are ashless oil lubricants without these additives, which can only fulfill the qualities of the previous generation with more expensive basestock and more expensive organic or organometallic additive compounds. Some new oils are not formulated to provide the level of protection of previous generations to save manufacturing costs. Some molybdenum disulfide containing additives to lubricating oils are claimed to reduce friction, bond to metal, or have anti wear properties. MoS2 particles can be shear welded on steel surface and some engine components were even treated with MoS2 layer during manufacture, namely liners in engines. (Trabant for example). They were used in World War II in flight engines and became commercial after World War II until the 1990s. They were commercialized in the 1970s (ELF ANTAR Molygraphite) and are today still available (Liqui Moly MoS2 10 W 40). Main disadvantage of molybdenum disulfide is anthracite black color, so oil treated with it is hard to distinguish from a soot filled engine oil with metal shavings from spun crankshaft bearing. In the 1980s and 1990s, additives with suspended PTFE particles were available, e. g., "Slick50", to consumers to increase motor oil's ability to coat and protect metal surfaces. There is controversy as to the actual effectiveness of these products, as they can coagulate and clog the oil filter and tiny oil passages in the engine. It is supposed to work under boundary lubricating conditions, which good engine designs tend to avoid anyway. Also, Teflon alone has little to no ability to firmly stick on a sheared surface, unlike molybdenum disulfide, for example. Many patents proposed use perfluoropolymers to reduce friction between metal parts, such as PTFE (Teflon), or micronized PTFE. However, the application obstacle of PTFE is insolubility in lubricant oils. Their application is questionable and depends mainly on the engine designone that can not maintain reasonable lubricating conditions might benefit, while properly designed engine with oil film thick enough would not see any difference. PTFE is a very soft material, thus its friction coefficient becomes worse than that of hardened steel to steel mating surfaces under common loads. PTFE is used in composition of sliding bearings where it improves lubrication under relatively light load until the oil pressure builds up to full hydrodynamic lubricating conditions. Some molybdenum disulfide containing oils may be unsuitable for motorcycles which share wet clutch lubrication with the engine.

Due to its chemical composition, worldwide dispersion and effects on the environment, used motor oil is considered a serious environmental problem. Most current motor oil lubricants contain petroleum base stocks, which are toxic to the environment and difficult to dispose of after use. Over 40% of the pollution in America's waterways is from used motor oil. Used oil is considered the largest source of oil pollution in the U. S. harbors and waterways, at per year, mostly from improper disposal. By far the greatest cause of motor oil pollution in oceans comes from drains and urban street runoff, much of it caused by improper disposal of engine oil. of used oil can generate a slick on surface water, threatening fish, waterfowl and other aquatic life. Toxic effects of used oil on freshwater and marine organisms vary, but significant long term effects have been found at concentrations of 310 ppm in several freshwater fish species and as low as 1 ppm in marine life forms.

Synthetic lubricants were first made in significant quantities as replacements for mineral lubricants (and fuels) by German scientists in the late 1930s and early 1940s, because of their insufficient quantities of crude needed to fight in World War II. A significant factor in their gain in popularity was the ability of synthetic based lubricants to remain fluid in very low temperatures, such as those encountered on Germany's eastern front, which caused petroleum based lubricants to solidify owing to their higher wax content. The use of synthetic lubricants widened through the 1950s and 1960s owing to a property at the other end of the temperature spectrum – the ability to lubricate aviation engines at high temperatures that caused mineral based lubricants to break down. In the mid 1970s, synthetic motor oils were formulated and commercially applied for the first time in automotive applications. The same SAE system for designating motor oil viscosity also applies to synthetic oils. Synthetic oils are derived from either Group III, Group IV, or some Group V bases. Synthetics include classes of lubricants like synthetic esters (Group V) as well as "others" like GTL (methane gas to liquid) (Group III +) and polyalpha olefins (Group IV). Higher purity and therefore better property control theoretically means synthetic oil has better mechanical properties at extremes of high and low temperatures. The molecules are made large and "soft" enough to retain good viscosity at higher temperatures, yet branched molecular structures interfere with solidification and therefore allow flow at lower temperatures. Thus, although the viscosity still decreases as temperature increases, these synthetic motor oils have a higher viscosity index over the traditional petroleum base. Their specially designed properties allow a wider temperature range at higher and lower temperatures and often include a lower pour point. With their improved viscosity index, synthetic oils need lower levels of viscosity index improvers, which are the oil components most vulnerable to thermal and mechanical degradation as the oil ages, and thus they do not degrade as quickly as traditional motor oils. However, they still fill up with particulate matter, although the matter better suspends within the oil, and the oil filter still fills and clogs up over time. So periodic oil and filter changes should still be done with synthetic oil, but some synthetic oil suppliers suggest that the intervals between oil changes can be longer, sometimes as long as primarily due to reduced degradation by oxidation. Tests show that fully synthetic oil is superior in extreme service conditions to conventional oil, and may perform better for longer under standard conditions. But in the vast majority of vehicle applications, mineral oil based lubricants, fortified with additives and with the benefit of over a century of development, continue to be the predominant lubricant for most internal combustion engine applications.

Bio based oils existed prior to the development of petroleum based oils in the 19th century. They have become the subject of renewed interest with the advent of bio fuels and the push for green products. The development of canola based motor oils began in 1996 in order to pursue environmentally friendly products. Purdue University has funded a project to develop and test such oils. Test results indicate satisfactory performance from the oils tested. A review on the status of bio based motor oils and base oils globally, as well as in the U. S, shows how bio based lubricants show promise in augmenting the current petroleum based supply of lubricating materials, as well as replacing it in many cases. The USDA National Center for Agricultural Utilization Research developed an Estolide lubricant technology made from vegetable and animal oils. Estolides have shown great promise in a wide range of applications, including engine lubricants. Working with the USDA, a California based company Biosynthetic Technologies has developed a high performance "drop in" biosynthetic oil using Estolide technology for use in motor oils and industrial lubricants. This biosynthetic oil American Petroleum Institute (API) has the potential to greatly reduce environmental challenges associated with petroleum. Independent testing not only shows biosynthetic oils to be among the highest rated products for protecting engines and machinery; they are also bio based, biodegradable, non toxic and do not bioaccumulate in marine organisms. Also, motor oils and lubricants formulated with biosynthetic base oils can be recycled and re refined with petroleum based oils. The U. S. based company Green Earth Technologies manufactures a bio based motor oil, called G Oil, made from animal oils.

A new process to break down polyethylene, a common plastic product found in many consumer containers, converts it into a paraffin like wax with the correct molecular properties for conversion into a lubricant, avoiding the expensive Fischer–Tropsch process. The plastic is melted and then pumped into a furnace. The heat of the furnace breaks down the molecular chains of polyethylene into wax. Finally, the wax is subjected to a catalytic process that alters the wax's molecular structure, leaving a clear oil. Biodegradable motor oils based on esters or hydrocarbon ester blends appeared in the 1990s followed by formulations beginning in 2000 which respond to the bio no tox criteria of the European preparations directive (EC/1999/45). This means, that they not only are biodegradable according to OECD 301x test methods, but also the aquatic toxicities (fish, algae, daphnia) are each above 100 mg/L. Another class of base oils suited for engine oil are the polyalkylene glycols. They offer zero ash, bio no tox properties, and lean burn characteristics.

The oil in a motor oil product does break down and burns as it is used in an engineit also gets contaminated with particles and chemicals that make it a less effective lubricant. Re refining cleans the contaminants and used additives out of the dirty oil. From there, this clean "base stock" is blended with some virgin base stock and a new additives package to make a finished lubricant product that can be just as effective as lubricants made with all virgin oil. The United States Environmental Protection Agency (EPA) defines re refined products as containing at least 25% re refined base stock, but other standards are significantly higher. The California State public contract code defines a re refined motor oil as one that contains at least 70% re refined base stock.

Motor oils were sold at retail in glass bottles, metal cans, and metal cardboard cans, before the advent of the current polyethylene plastic bottle, which began to appear in the early 1980s. Reusable spouts were made separately from the cans; with a piercing point like that of a can opener, these spouts could be used to puncture the top of the can and to provide an easy way to pour the oil. Today, motor oil in the US is generally sold in bottles of and on a rarity in as well as in larger plastic containers ranging from approximately due to most small to mid size engines requiring around of engine oil. In the rest of the world, it is most commonly available in 1L, 3L, 4L, and 5L retail packages. Distribution to larger users (such as drive through oil change shops) is often in bulk, by tanker truck or in drums.

Human ingestion of motor oil is considered dangerous. Ingestion of small amounts unused motor oil will generally result in loose stools or diarrhea. The motor oil could also aspirate (go down the wrong way). This can cause: coughing, wheezing, or trouble breathing. If the skin comes in contact with motor oil defatting can occur. If exposed to an open flame motor oil could ignite.