Conventional and Synthetic Oil Technology Explained
RRT’s research into the many times confusing and technical world of motor oil technology has led to some very important findings. But first, we would like to give you an overview of some of the technical aspects of motor oil technology. These are important points to understand, but our descriptions are brief enough so that you do not get overwhelmed in technical jargon.
What do those “W” numbers mean?
The Society for Automotive Engineers (SAE) has a set of standards by which the world grades all motor oils. Straight-weight oils, such as SAE 30, are graded SAE 30 due to their viscosity measured at 100oC. Oils with two numbers, such as 5W30, are called multi-viscosity oils. For example, 5W30 is actually an SAE 30 weight oil. However, since regular SAE 30 weight oil is quite thick when cold, the multi-viscosity oil was invented to make sure an oil is not too hard to pump through the engine when very cold, but still thick enough that it lubricates well when the engine is up to temperature.
The first number in a multi-viscosity oil grade is a measure of its ability for a metal shaft to rotate inside a container of oil when chilled to a specific temperature. Basically, it is a measure of the cold weather performance of an oil. A 0W oil is tested at a lower temperature than a 5W or 10W oil, and the metal parts must be able to move better in the 0W oil at that lower temperature. The second number or SAE grade is a measure of the viscosity at 100oC / 212oF. To be graded as a 30-weight oil, it must be within a specific viscosity range at 100oC. A 15W50 oil is a 50 weight oil with a 15W rating when cold.
Think of the first number as being a “Winter” classification, and avoid associating the W number as a viscosity rating when cold. Viscosity/weight is measured at 100oC, so saying an oil has a certain viscosity when cold is a misuse of the terminology. So when someone says, “15W50 oil is like having a 15 weight oil when cold and a 50 weight oil when hot,” that is technically not the case. A 15W50 oil is still a 50 weight oil but has a cold weather performance of “15 Winter,” which is a measure of its resistance to pumping and motion during cold startup.
Petroleum based conventional oils
Conventional oils come from crude oil pumped from the ground. The refining process removes unwanted contaminants over several stages, resulting in a basic lubricant that forms a slippery layer between engine parts to prevent metal-to-metal contact. Additives are used to lower the temperature at which they pour when very cold. Additives are also used to boost their viscosity as the oil heats up. Remember that most liquids, especially petroleum oil, get very thick when cold but thin out significantly when heated. Considering you may see temperatures well below freezing during startup, and some surfaces inside the engine can reach over 300oF even when driving in Alaska, it is easy to see that any engine oil must lubricate well at very low temperatures as well as very high temperatures.
Synthetic Oils represent a category that would be difficult to cover briefly, but here are some basics you must know. There are 3 major types of synthetic oils available for lubricating everything from your lawnmower to a BMW Rolls-Royce turbine engine in a passenger plane. The first is what is called a Group III oil, which starts off by being pumped out of the ground as crude oil, just like standard petroleum oil. It undergoes the same refining processes as petroleum oil, but is then taken a few steps further by being broken down into smaller molecules and reformed in a lab manufacturing environment. These extra steps reduce or eliminate many of the unwanted contaminants found in standard petroleum oils. These oils were previously not considered true synthetic oil until a lawsuit between two major oil companies resulted in Group III oils being classified as true synthetic. They are good oils which do not possess many of the problems associated with petroleum oils. Castrol Syntec and Mobil 1 are both Group III synthetic oils, as are most of the store-bought and lower priced synthetic brands.
The second type of synthetic oil is called a Group IV or PAO oil. PAO stands for PolyAlphaOlefin, which is the base stock. This base stock is also made from crude oil pumped from the ground, but that is about all it has in common with petroleum or Group III oils. The refining process separates very specific small molecules (olefins) from the crude oil, which are harvested and then combined in a lab to form very uniform oil molecules. In other words, the base stocks are completely manufactured in a lab, but the stocks are made from molecules taken from crude oil. PAO oils are free of unwanted contaminants such as wax, sulphur, and other metals. The uniformity of the molecule is very important when it comes to the final product and its ability to lubricate at 0oF or 300oF. The Motul 8100 X-cess oils and the BMW Specific Long Life 01 oils are Group IV PAO based oils.
The third type of synthetic oil is called an Ester based oil. Esters, diesters, and complex esters are formed in a lab from vegetable and animal fats, and they do not come from crude oil. These oils undergo the most strictly controlled manufacturing processes, and as a result, are the highest quality oils available. Jet engines, turbines, and the world’s highest performance racing engines use only ester oils for lubrication, since they are the most resistant to vaporization, high shear and thermal breakdown. Turbines spin at many thousands or tens of thousands of revolutions per minute and see internal temperatures that would destroy ordinary oils in seconds. Formula 1 engines also see extreme temperatures and nearly 20,000 RPMs. Motul’s line of 300V and 8100 E-tech oils are 100% Ester based and are designed for both heavy duty and racing use.
Additives exist in both petroleum and synthetic oils. Some additives are used to modify the viscosity and pouring abilities of motor oil. There are additives to prevent the oil from becoming too acidic over time, to surround dirt particles and keep them trapped in the filter, to prevent wear when metal to metal contact does occur, and to perform a host of other duties. Since petroleum oils are simply refined crude oil, they still contain many components that are highly undesirable. One of these is paraffin or wax. Wax thickens significantly when cooled, and it traps useful oil molecules in the process. Additives called pour-point depressors are used to cling to the wax molecules so the useful lubricant oil does not become trapped. On the other end of the spectrum are the Viscosity Index Improvers, or VIIs. VIIs are long-chain polymers (molecules that are made of many atoms in a long chain) that are coiled up when cold, but expand to full length when heated. These long molecules are what make sure a petroleum oil can stay “thick” enough to lubricate when subjected to high temperatures.
Nearly any synthetic oil will perform significantly better than the best petroleum oil you can buy. Since synthetics are manufactured in highly controlled processes, they have more uniform molecules that require little or no Viscosity Index Improvers or pour-point depressors, while conventional oils use them heavily. Due to their long-chain nature, VIIs are torn apart by high temperature and high shear loads experienced within any modern engine. And every time the oil gets cooled significantly, pour-point depressors are actually used up. Over time, petroleum oil becomes thicker and harder to pump every time it gets very cold. High temperatures cause the lighter molecules in conventional oil to vaporize, where the crankcase ventilation system (PCV) sucks them into the combustion chamber to be burned. What is left after the VIIs are broken down, the pour-point depressors are used up, the lighter oil molecules are vaporized and burned off, and the weaker, heavier oil molecules are broken down from high temperature / high shear (HTHS)? Well, you can probably guess that what is left does not do a very good job of lubricating or keeping your engine clean inside.
A few words on ‘snake oil’ and other magical oil additives
An oil is only as good as the base stock and additive package. Higher quality synthetic oils contain very balanced additive packages with high quality ingredients. There are plenty of aftermarket oil additives that promise reduced wear, lower temperatures, and better gas mileage, but many of them are just high doses of additives that are already in the oil you buy off the shelf. Some oil additives such as phosphorus and zinc can reduce high-pressure wear or prevent damage when metal to metal contact occurs, but too much phosphorus and zinc will harm your oxygen sensors and catalytic converters! Current oil standards actually restrict the amount of zinc and phosphorus that an oil can contain. Teflon based oil additives do nothing for metal parts, since Teflon does not bond to metal at any temperature that the inside of your engine will ever see. One brand of oil additive on the market is simply tinted mineral oil! Additionally, many oil additive companies have been brought up on charges by the Federal Trade Commission for false advertisement and failure to support their claims. Caveat Emptor! Buyer beware! Do not rely on some marvel substance to turn bottom-dollar oil into a premium lubricant. Additionally, do not add any aftermarket additives to your expensive synthetic, since they can actually cause damage to your engine or upset the balance of additives the oil manufacturer has carefully selected.
What does this all mean?
First and foremost, use a premium synthetic oil. German, Japanese, and even some American car manufacturers are recommending very long drain intervals for even the highest performance vehicles they sell and have been selling for many years. The typical BMW oil service interval (as indicated on the instrument cluster) can be up to 12,000 miles! This oil change interval is practically impossible with any standard petroleum motor oil. Yes, you can change your oil more often than every 7,000-12,000 miles, but is it necessary? With a premium synthetic backed up by oil analysis, it will most likely be a waste of good oil and hard-earned money to change your oil on the old standby of 3 months or 3,000 miles. Oil analysis is relatively inexpensive and can confirm that the oil is fine for use or should be changed. It also can determine the presence of many contaminants in your engine oil: coolant, fuel dilution, wear metals such as engine bearings, dirt particles that pass by the air filter, and also oil filter efficiency.
Other aspects of oil performance such as flash point, fire point, pour point, Viscosity Index (VI), Total Base Number (TBN), etc, are all important in both the daily commuter and racing engines.
- Flash point determines at what temperature an oil will vaporize and catch fire when exposed to a flame, while fire point is the temperature at which the oil will sustain a fire on its own.
- Pour point is the temperature 5oF above which a pool of oil will not appear to move after 5 seconds when placed on an incline. If the oil does not appear to move when placed on an incline at -40oF for 5 seconds or more, the pour point is considered to be -35o
- Viscosity Index is a measure of how well the oil resists thickening at low temperature but also resists thinning at high temperature. Basically, the Viscosity Index is a measure of how well an oil holds its viscosity over a wide temperature range. The higher the number, the better.
- TBN is a measure of how much acid-neutralizing base is present in the oil. Petroleum oils are not meant for extended use, so they do not have as high TBN as synthetics. TBN for petroleum oils is typically 5 to 8, while premium synthetics range from 9 to 14 TBN.
Conventional petroleum oils such as 10W40 and 5W30 will have VIs above 100 but typically below 140, where PAO and Ester based synthetics score at least 140 or much higher. Petroleum oils burn at much lower temperatures, showing flash points in the low 400oF range, while premium synthetics show flash points well above 430oF to 470oF. Premium synthetics typically have pour points 20-40oF lower than equivalent weight petroleum oils. It is easy to see that premium synthetics outperform petroleum oils in all categories.
Motul oil is a full line of premium synthetic oils that are the best for not only the typical day-to-day commuter, but also the track car that gets driven hard 5-10 weekends per year at races and driver schools. Motul uses PAO based oils for the 8100 X-cess line, while the 300V line and 8100 E-tech (short for “Ester-technology”) are made from Esters. Ester based oil molecules also carry the added benefit of having an electrical charge. One side of the molecule has a positive charge, while the other has a negative charge. This means that ester based oil molecules are always going to build up a layer of protection between metal parts during cold starts. The 8100 X-cess, 8100 E-tech and 300V oils are the highest performance lubricants available today. In fact, Motul led the way in 1972 with the first ester based oil for vehicle use, and still leads with the introduction of Double Ester technology (Esters, polyolesters, and other complex esters combined) in 2004.
To match the extended drain intervals seen on European cars since the early 90s, the oil must have balanced additive packages and be able to withstand high temperatures, low temperatures, high loads and high engine stresses, and still be able to maintain reliable engine service at or over 200,000 miles. Motul oils meet or exceed the European ACEA (Association des Constructeurs Europeens d’Automobiles) standards for high performance and extended drain oils (ACEA A3/B3) and American Petroleum Institute (API) standards for high performance oils (API SH). Motul 8100 X-cess oils meet or exceed many existing manufacturers’ specs including BMW, Volkswagen/Audi, Porsche, and Mercedes Benz. For engines that require specific formulations, Motul also has a line of premium synthetics that carefully match the manufacturers’ requirements for BMW, Mercedes, VW, and Ford. For racing engines or highly modified and turbo- or supercharged engines, the 300V oils offer the ultimate protection during cold startup and high temperature and high stress levels seen under the most grueling 24-hour endurance races. The 300V line is available in weights from 0W20 for sprint and drag racing up to 20W60 for endurance racing.
Depending on the age of your vehicle, oil analysis may be needed to ensure your current oil change intervals are on target, or whether you should extend or reduce the time between oil changes. For most vehicles that have seen regular maintenance in the past, switching to Motul synthetics requires nothing more than a simple oil and filter change. Only engines that are more than 20 years old or have very high mileage (usually over 150-200k miles) should be checked before switching to synthetics. Some older engines with existing oil leaks or aging seals may suffer additional oil leak issues when switching to any brand of synthetic oil.
What about the rest of the fluids?
Motul’s line of gear oils covers nearly all types of transmissions used in street and racing vehicles. The synthetic base stocks used in Motul gear oils resist breakdown from shearing stresses and high temperatures. Gear 300 is an ester based 75W90 gear oil that meets GL-4 and GL-5 standards, which makes it an excellent choice for limited slip differentials and manual transmissions, and also manual transaxles found in Porsches, Subarus, Audis, and 1997 and later Corvettes. For heavily loaded differentials, gearboxes, and transaxles, Motul Gear Competition FF is also an ester based 75W140 gear oil, but it has been specifically formulated for the extreme temperatures and stresses seen in racing and track driving or even with high horsepower adders such as turbos and superchargers.
For the modern brake system, Motul has formulated a DOT 5.1 brake fluid that features very high dry and wet boiling points, low viscosity for enhanced ABS and traction control operation, and extended flushing intervals (2 to 3 years). For track use, Motul RBF600 is an ultra-high boiling point fluid (593F dry) that is perfect for brake systems that see extreme temperatures from racing.
Motul Inugel coolants are coolants that are free from phosphates, nitrates, and amines, which eliminates contaminant build-up in the coolant system. Motul Inugel Expert Ultra is concentrated and must be mixed with soft or distilled water to at least a 33% concentration. Since Motul Inugel Expert Ultra offers superior freezing and boilover protection over Original BMW coolant, we recommend a 40-45% concentration of Inugel coolant in distilled water. This equates to 3 Liters of Inugel coolant to 1-1.2 gallons of distilled water.