This is a combination of oil tech related blog posts I wrote back in 2012.
Acids & Bases
Let me preface this first installment of our Oil Tech series by saying I am definitely the engineer type, and the years I’ve spent in the automotive industry have led me to ask a lot of questions about how things work and why things happen. So, how does the oil in your engine work? As i learn more about lubricants and their properties, I’ve become almost overwhelmed by the complexity of the duties the oil in your engine performs. Each new post will discuss another important factor in your oil’s performance, longevity, potential issues, or just things I find cool about lubricants.
Why does oil wear out? A good question that has crossed the mind, at some point, of almost every automobile owner on the road. As I mentioned, there are several things that affect your oil’s ability to perform. Today we will address a property known as stability.
Oil stability is, just as it sounds, the ability of the oil to remain stable. What does that mean? The combustion process is a complex mix of chemistry and thermodynamics. The combination of the byproducts of combustion, namely heat and gasses, work together to create a very harsh environment for your engine oil. This can have many negative effects on the oil, but today we will be focusing on oxidation and acidity.
When oil oxidizes it creates carboxylic acid. In some engines, the presence of sulfur (more common in diesels) can also combine with combustion gasses to create sulfuric acid. Either way, the presence of acids in the oil is not good, as acids are corrosive and can react with the metals in your engine.
This is addressed by adding a base to the oil to neutralize the acid. Typically the added base would be an alkali metal or alkaline earth metal, and the measurement of base in the oil may be referred to as alkalinity. This would be part of the additive package in the oil, and calcium is a popular antioxidant/anti-corrosive additive in lubricants.
The best way to test how much life is left on an oil is to have an oil analysis done where the TBN, or Total Base Number, is measured. Just as it sounds, this is a measure of the reserve alkalinity, or how much acid-neutralizing capacity the oil still has.
There are also several oil additives that have increase the TBN, most of which contains calcium, among other lubricating and detergent additives.
One property of engine oil that most people are familiar with is the grade. Oil grade is sometimes referred to as weight, and oil grades are measured using a standardized test developed by the Society of Automotive Engineers (SAE) and are outlined in the document SAE J300.
SAE J300 defines separate testing methods for standard weights (20, 30, 40, 50, and 60) and winter weights (0W, 5W, 10W, 15W, 20W, 25W) based on the oil’s performance without viscosity modifiers. Standard oil weights are determined based on the kinematic viscosity low shear rate at 100 °C , as well as the minimum dynamic viscosity high shear rate at 150 °C. The winter grades are based on a test designed to simulating cold cranking and the grade is determined based on the lowest temperature it meets the dynamic viscosity criteria, with lower grade numbers relating to colder temperatures. This is why you would use a 5w instead of a 10W in colder climates. Multi-grade oils weights (ie, 5W40, 10W30, etc) are used to designate oils that meet both the standard and winter weight criteria as outlined in SAE J300. It should also be noted that the criteria for grading gear oils (75W90 and the like) use a completely different scale.
So, what is viscosity? Dynamic viscosity, or absolute/simple viscosity, is the measure of a fluid’s ability to resist deformation in the presence of shear stress, or the resistance to movement of the layers of a fluid when subjected to a force. Kinematic viscosity is defined as a measure of a fluid’s resistance to flow or deformation, or, essentially, the thickness of a fluid. The higher the kinematic viscosity, the more resistant it is to flow, thus, the slower it will flow. For example, molasses or honey would have a higher kinematic viscosity than, say, water. Kinematic viscosity is also defined as the dynamic viscosity divided by the density.
Another important variable regarding engine oil, also developed by SAE, is viscosity index. Viscosity index is an arbitrary measure of how the viscosity changes with temperature. Without getting into too many details, it is a number from zero (worst) to one hundred (best), although advances in lubricant technology have led to the formulation of oils have a viscosity index over one hundred, thanks to viscosity modifiers.
As you probably assumed, viscosity modifiers improve the viscosity index of engine oils. Most multi-grade oils use viscosity modifiers to allow good cold temperature (cranking) flow while not allowing them to thin out at high temperatures. It could be said that a 5W40 oil essentially acts like a 5W weight oil when cold that will not thin out more than a 40 weight oil at temperature. Viscosity modifiers are typically certain types of polymers or olefins.
Another viscosity-changing oil additive that is sometimes used is called a pour point depressant. This improves the cold flow characteristics of the oil. Specifically, it decreases the lowest temperature at which the oil will flow, which improves the cold-starting/cranking flow of the oil. This is used because petroleum-based oils contain paraffin (waxes) that solidify/crystallize at low temperatures. Pour point depressants inhibit wax precipitates from forming by inhibiting crystal formation. Some common pour point depressants are alkylated napthalene (similar to the stuff in mothballs), esters, phenols, or certain polymers.
Considering how important the viscosity of your engine oil is to maintaining proper oil pressure and resisting wear of engine components, it is not surprising that so much technology goes into precisely dialing in the oil’s viscosity over the entire range of temperatures you would expect to see, from when you first crank all the way to operating temperature. Viscosity is just one characteristic related to your oil accomplishing the complex range of duties expected of it on a daily basis.
While non-detergent oils are comprised of only oil base stock, most engine oils on the market today contains several components, but they can all be classified into one of two basic categories: the base stock, which I will discuss here, and the additive package, which will be discussed in other oil tech articles (see the link at the bottom of the page).
Oil base stocks are classified based on criteria outlined by API, the American Petroleum Institute, and fall into one of the five groups, numbered one through five. Every engine oil will fall into one of the five categories, with Group V being a catchall for everything not meeting the criteria for the other four groups. Groups I and II are mineral oils, your basic petroleum based oil, and are divided, roughly, based on the amount of processing. Group III is a highly-processed petroleum based oil, and is considered a synthetic oil throughout most of the world. Group IV is a fully synthetic oil that uses a PAO base stock. Group V oils have such a wide variety of base stocks, it cannot be classified either way, and, again, is a catchall for all oil base stocks not comprised of mineral-based oils or PAO oils.
Group I base stocks contain less than 90 percent saturated hydrocarbons, also called saturates, alkanes, or paraffins, less than 0.03 percent sulfur, and have a viscosity index (refer to tech article on viscosity) between 80 and 119, inclusive. Group I base stocks contain fractionally distilled petroleum that is processed with solvent extraction techniques to remove waxes and increase oxidation resistance. Group I base oils contain a significantly higher amount of impurities when compared with Group II oils, and are not used in modern conventional oils.
Group II base stocks contain over 90 percent saturated hydrocarbons, less than 0.03 percent sulfer, and have a viscosity index between 80 and 119, inclusive. Group II base oils are also created from fractionally distilled petroleum, much like Group I base stocks. The biggest difference between Group I and Group II base stocks is the type of processing performed. Group II oils are subjected to a variety of hydroprocessing techniques, including hydrotreating, hydroisomerization, hydrocracking, and hydrofinishing, all of which will be discussed further in future articles. These processes strip wax, remove impurities, further refine the base stock by reshaping the oil molecules. The result is a mineral based oil with fewer impurities and much higher quality than the outdated Group I base stocks.
Group III base stocks contain over 90 percent saturated hydrocarbons, less than 0.03 percent sulfer, and have a viscosity index over 119. The defining difference between a Group II and Group III base stock is the viscosity index, with Group III oils having an “unconvential” viscosity index, and, as a result, Group III base stock are sometimes called unconventional base oils (UCBO) or very high viscosity index base oils (VHVI). Group III base oils are processed similarly to Group II oils, with the main difference being either a more severe hydrocracking process or higher grade feed stock, resulting in the improved viscosity index. Modern Group III base stocks can match or exceed the performance of Group IV PAO oils, and can be labeled and marketed as synthetic oil in the United States, as well as most of the world, with the exception being Germany and Japan. The reasoning is that a Group III base stock is processed, and its chemical composition altered, so extensively that it no longer resembles a mineral oil, such as Group I or Group II.
Group IV base stocks are made up of polyalphaolefins (PAO). Beyond that, API does not set forth any standards for viscosity index. Group IV oils are what is traditionally referred to as synthetic. Polyapthaolefins are created by, no surprise, polymerizing and alpha-olefin. Without getting into too much organic chemistry, it basically results in an oil that has smaller molecules, rather than long hydrocarbon chains, as you would find in a traditional mineral oil. Group IV oils are generally more expensive than Group III oils simply due to the cost of manufacturing associated with PAO production. While Group III oils can now be created with similar performance characteristics to Group IV oils (more on that later), PAO oils do, generally, have a lower pour point, making them superior in colder conditions, although there are pour point depressant additives today that help close that gap.
Group V base stocks are all oil base stocks not classified under Groups I-IV. These are typically created using a polyol ester (POE) or other esters, polyalkylene glycol (PAG), but Group V oils could be any oil that is not created from distilled petroleum or PAO. These are not as common in engine oil applications, and POE/PAG oils are more commonly found as a compressor lubricant in refrigeration systems, such as your car’s air conditioning system. There are, however, some ester-based engine oils on the market today.
There is a lot of controversy as to what can and cannot be called synthetic. As was mentioned earlier, in most of the world, Group III base oils are allowed to be labeled and marketed as synthetic. Up until 1999, it was the general consensus that only Group IV oils were fully synthetic. That changed when the National Advertising Department of the BBB decided that Group III oils could be considered synthetic. So, whether or not the oil is a PAO synthetic, highly refined and processed mineral oil, or a combination of the two, it can be labeled as synthetic at your local parts store.
With today’s technology, Group III and Group IV oils are both very high quality engine lubricants that will stand up to the extreme conditions of your engine’s crankcase. The most important factor in determining which oil is right for your car is not the type of base stock used, but, rather, whether it has been approved by the manufacturer to meet the criteria of the oil specification for your specific engine.
One of the most dangerous substances to an engine’s lubrication system is oil sludge. Anyone who is familiar with Volkswagens and Audis knows that the early 1.8t engines (AEB) that came in Passats and A4s have a notorious engine oil sludge problem. VW’s fix is to use a larger filter, the one for earlier diesel engines, which adds approximately a half-liter of oil capacity.
Oil sludge can wreak havoc on an engine. In the case of the aforementioned Passats and A4s, an engine with a sludge problem is a fairly expensive fix if caught soon enough, and has the potential to be very expensive if the problem is overlooked for any significant amount of time. Initially, the sludge will clog up oil passages in the engine block and cylinder head, the oil pickup tube attached to the oil pump, and the oil lines providing lubrication to the turbocharger. If the issue is not addressed in a timely manner, the sludge will severely restrict oil flow to the engine and turbocharger, which could potentially ruin the turbocharger bearings, the engine crankshaft and connecting rod bearings, and the cam journals in the cylinder head. It can also accumulate on the piston ring lands (the notch where the piston ring sits) and restrict movement of the rings, which can result in accelerated wear of the rings and cylinder wall, loss of compression, broken rings, etc. In short, an unchecked oil sludge problem can result in serious damage requiring engine and/or turbocharger replacement.
On a side note, this is very common on the AEB engines, and anyone looking to upgrade to the better-flowing “big port” AEB cylinder head should pay special attention to cam journal wear. The repair manual states that the cam journal clearance wear limit is 0.1mm, measured using plastigauge with the cam followers not installed.
Oil sludge refers to a nasty substance that forms in the oil, and can range in color from light brown to black and in texture from gooey to almost solid. It can form for a number of reasons, and typically the color and texture will help to diagnose the issue. We will divide the reasons into two basic groups: water/coolant intrusion and oil breakdown.
Water or coolant in the oil will typically cause a gooey light brown sludge resembling a chocolate milkshake in appearance. Coolant intrusion is exactly what it sounds like, coolant in the oil, and is typically the result of a leaking gasket, such as the cylinder head gasket, but can also result from a faulty oil cooler. Water can get into the oil, as well. Typically this would be the result of condensation, and becomes prevalent on vehicles that do not properly get up to operating temperature, thus, not producing enough heat to properly evaporate the condensation from the crankcase. This occurs most often on vehicles that are only taken on short trips or due to a faulty (stuck open) thermostat.
Sludge resulting from breaking down the oil is usually thicker and darker. It can be tar-like or almost rock hard, and is usually black. Oil breakdown can also occur for several reasons. As discussed in the Acids & Bases section, heat and combustion gasses, usually resulting from blow-by, can cause the oil to break down. The blow-by can also contain a number of contaminants, such as unburnt fuel, dirt, or soot. While modern engine oils contain detergents and are chemically basic (pH over 7), over time, contaminants and acids that enter the oil, along with heat, can neutralize the oil and consume the detergents.
This is why it is important to maintain a regular, reasonable oil change interval with a high quality oil that meets the manufacturer’s specifications. Removing the contaminants and acids from your engine will prolong the life of the engine, not only by reducing the potential for corrosion or wear due to dirty oil, but also by reducing the potential for engine sludge. In addition to regular oil changes, keeping the PCV system functioning properly will help alleviate corrosive blow-by gasses and moisture from remaining in the crankcase.
It should be noted that, for vehicles that are used for a lot of stop-and-go driving, idle for long periods, or are subjected to heavy duty use, such as high engine temps, heavy loads from hard driving or towing, or are operated in dusty areas, a shorter oil change interval can help keep oil sludge at bay.
In short, the best way to keep your engine’s lubrication healthy and strong is to maintain it properly with manufacturer approved oils. If you are looking to extend your oil change interval or check that it is proper for a vehicle that sees heavy use, an oil analysis can provide insight into how much life is left in your oil.
Previous sections in this article focused on the physical and chemical properties of engine oil, as well as some of the conditions that cause oil to break down, become acidic, and form sludge. While all of this is good knowledge, it is also important to understand all of the ways the oil in your engine functions to ensure proper lubrication, minimize wear, and keep your engine running smoothly.
The most important function of the engine oil is to provide lubrication. Basically, there are two different ways this happens: by creating a pressurized film within bearing journals and by creating an oil film between non pressurized surfaces.
Pressurized bearings rely on oil pressure to create a thin film between two surfaces. This type of bearing is found on rotating parts in the block and cylinder head, such as the crankshaft main bearings, rod bearings, and camshaft journals/bearings. The oil pump lubricates these bearings by sending pressurized oil through the galleries, which is then pumped into the bearing through holes in the main crankshaft journals or camshaft journals. The rod bearings are lubricated through channels through the crankshaft, which transfers the pressurized oil from the main bearings journals to the rod bearing journals. In some cases, the piston wrist pin also receives pressurized oil through rifle-drilled channels that run through the connecting rod. In other cases, the wrist pin receives oil through splash oiling through holes in the wrist pin end of the connecting rod. Pressurized bearings rely on the viscous properties of the oil to create film strength, which allows the inner bearing to float inside the outer bearing.
The oil also lubricates non-pressurized surfaces in the engine, such as the contact patch between the cam lobe and the cam follower or the piston ring and cylinder wall. Since the contact surfaces are in contact with each other, lubrication becomes very important. Additionally, wear becomes an issue, and this is the main reason for anti-wear additives and extreme pressure additives such as zinc, phosphorus, and molybdenum (more on this in a later article).
Where the piston ring is constantly sliding up and down, the cylinder cross hatching plays an important role in maintaining an oil film by creating tiny crevices to hold the oil. Oil on the cylinder wall/piston ring contact surface is also important for creating a strong seal to hold the engine compression within the combustion chamber.
While lubrication of moving parts is the most important function of the oil within the engine, your oil also performs other vital functions by providing corrosion and oxidation resistance for metal parts, cooling engine parts and transferring heat away from the pistons, sometimes by using oil squirters that spray the bottom of the piston. The oil additive package will also contain detergents to help keep the engine clean and minimize sludge and varnish and seal conditioners, as most seals would deteriorate at the temperature the engine operates without them.
Overall, the oil truly is the lifeblood of the engine, performing many vital functions to keep the engine operating smoothly and cleanly for years.
In some of the other Oil Tech articles I briefly touched on some oil properties such as total base number (the measure of remaining acid-neutralizing capability of the oil) and viscosity. There was also a brief mention of the additive packages that, in addition to the base stock, make up engine oil.
One common question that goes along with these things is “How do i figure out how much life is left in my oil?” or “Is it ok to extend my oil change interval?” Both of these questions can be answered with an oil analysis.
We typically use Blackstone Labs, which is one of several companies that offers a variety of oil analysis procedures. Pricing is reasonable at $25 for a standard oil analysis, which uses a spectrometer to measure the level of metals, additives, and silicon present in the oil. Blackstone Labs will also measure some of the physical properties of the oil such as flash point, viscosity, and percentage of insoluble solids present. Measuring the total base number (TBN) is an additional $10. They also offer a variety of other tests which are listed, with pricing, on their website.
The spectrometer results can be very helpful in diagnosing what exactly is going on in your engine. The levels of common additives, such as calcium, phosphorus, and zinc, will give you an idea of how depleted the additive package in the oil has become. The levels of wear metals can give you an idea of the condition of things like your bearings and piston rings. For example, if you see an elevated level of copper or aluminum, it may indicate bearing wear. On the other hand, piston ring wear may show up as elevated chromium levels.
The Blackstone Labs analysis report will also have an explanation of what the different levels may indicate, recommendations as far as extending your oil change interval (may require TBN test), or things to keep an eye on in the future. Regular oil analyses will give you an idea of how these levels have changed over time and allow you to track the condition of the parts inside your engine.
They do ask for some of the vehicle information, such as make, model, engine, mileage, etc. All of the times I have spoken with them directly, they were very knowledgeable about some of the common problems with the engine in question, such as the issues with camshaft wear in some of the TDI (turbocharged, direct-injection, diesel) engines.
All in all, an occasional oil analysis is a good way to stay aware of the condition of your engine as well as your oil. It is a great way to keep an eye on wear and potentially prevent damage. It is always easier to solve a problem when you know that the problem exists and what that problem is.
The base stock section explained the different types of base stocks, how they are classified, and the benefits and drawbacks of each. This article will focus on the other component of motor oils, the additive package.
There are many different additive types, so many it might make your head spin, but they can be categorized by the basic function: extending oil life/controlling contaminants, modifying viscosity, modifying lubricity, and conditioning seals.
There are several reasons for extending oil life. Not only is it better for the engine to keep the oil stable, it also reduces maintenance costs when the oil change intervals can be extended safely. Detergents (such as boron, calcium, magnesium, and barium) neutralize acids in the oil (a result of combustion heat and gasses) and dispersants (long-chain hydrocarbons) keep contaminants suspended in the oil. This allows the contaminants to be removed when the oil is changed instead of settling inside the engine oil passages and pan. Corrosion inhibitors (alkalines, esters, organic acids) keep the engine’s oil passages free from rust and corrosion and antioxidants (amines, phenols, sulfides) keep the oil stable and prevent oxidation (breakdown) of the oil. Oil oxidation is one of the biggest causes of sludge. Other additives whose purpose is to extend oil life deactivate wear metals, keep the oil from foaming (dimethylsilicone) and misting, and modify the wax crystals in the oil.
Viscosity modifying oil additives (acrylate polymers) allow multi-weight oils to be produced (such as 5w40) by changing the viscosity index and keeping the oil viscosity more consistent across the temperature range. This includes pour point depressants, which thin the oil at low temperatures by preventing the formation of wax crystals at low temperatures.
Some of the most critical additives for engine longevity are lubricity/friction modifiers. Friction modifiers are typically solid lubricants (graphite, molybdenum disulfide, boron nitride, PTFE, etc) that lower the coefficient of friction of the oil. One of the biggest benefits of friction modifiers is lower fuel consumption. Extreme pressure agents (molybdenum disulfide, ZDDP, esters, etc) and anti-wear agents (ZDP, ZDDP, TCP) prevent lubricated metal surfaces from contacting one another. These agents create a lubricating film which reduces wear, scuffing, and scoring. Zinc (ZDDP) and phosphorus based anti scuff additives have been limited by the American Petroleum Institute due to the potential for damaging the catalyst in modern catalytic converters. Break in additives and break in oil contain significant amounts of this type of additive, but they are designed for short-term use which allows conventional oil to be used for break in while preventing damage to valvetrain components.
Another popular oil additive is a seal conditioner. Seal conditioners prevent silicone seals from breaking down due to heat and cause gaskets and seals to swell slightly to ensure a tight seal, preventing oil leakage.
While modern engine oils contain a base stock and an additive package, which contains several different types of the additives outlined above, oil additives are available separately. Most popular oil additives are, essentially, a concentrated mixture of friction modifiers, anti-scuff and extreme pressure agents, detergents, dispersants, and antioxidants. It is recommended for use in engines with extended oil change intervals.