Editor's Note: This is Part One of a special Sport Rider comparison test, where we unlock the mysteries and debunk some of the myths of motor oil. We examine just what goes into motor oil, why those ingredients are there and what it means for your engine. In the next issue, Part Two will feature a scientific analysis of all major motorcycle-specific motor oils, plus a wear and dyno test of specific oils to determine whether there is a power difference.
When motorcyclists discuss engine oil, they quickly polarize into two groups. There are those who think all oils are basically the same, and that anyone spending more for premium oils is wasting his money, and there are those who feel there is a difference and are willing to spend the money to get the best product available. However, both groups share a lack of scientific information allowing them to make an informed decision. To offer some insight into this heated topic and help you determine which oil is right for you, we've decided to delve into this outwardly simple-but very complex-product. In Part One of this two-part series, we'll dissect the real what, how and whys of motor oil.
The first thing you need to know about motor oil is what it does for your engine. Motor oil actually has several purposes, some of which may surprise you. Obviously, lubrication is the main purpose. The oil serves as a layer of protection between the moving parts, just like shaving gel does between your skin and a razor.
However, oil also acts as a dispersant, which means it holds damaging stuff like dirt and metal particles suspended in the oil (rather than letting them settle to the bottom of the oil pan where they can be recirculated through the engine) so they can be removed by the oil filter. Then there is the job of corrosion retardant. By reacting with the nasty acids created by combustion, oil actually prevents these byproducts from damaging the internals of the engine. For instance, when combustion takes place, sulfur molecules in gasoline occasionally combine with air and water molecules, forming a vile brew called sulfuric acid. Left unchecked, this acid will eat away at internal engine compounds. Good oils, however, contain enough of the right additives like calcium, boron or magnesium to neutralize these acids.
Cooling is another important factor. Oil serves to cool hot spots inside an engine that regular coolant passages cannot reach. Since coolant usually only deals with the hottest parts of the engine, like the cylinders and cylinder head, there are many internal engine components that depend on oil for cooling as well as lubrication. For example, the transmission and clutch rely heavily on oil to regulate temperatures, since excessive heat expansion can change tolerances and cause clearance-related problems. Another area that uses oil for cooling purposes is the undersides of the pistons; with pistons becoming thinner for less weight, yet dealing with ever-increasing compression ratios, keeping the piston assembly cool is vitally important. Parts such as these can expose oil to extreme temperatures, so this is one reason that thermal stability is so important for motorcycle engines. We will do a specific test in Part Two to predict the oils' ability to survive in extreme heat.
Who is the API?
The American Petroleum Institute (or API) was established in 1919 as an industry trade association with one of its goals stated as "promot(ing) the mutual improvement of its members and the study of the arts and science connected with the oil and gas industry." Today, the API impacts the consumer market through the development and licensing of engine oil industry standards. On most oil containers, you will find a small circular label that says "API" along with letters like SG, SH, etc. Each of these letters represents a very complex set of specifications and tests that have to be met in order for an oil to carry the API designation. When you see an oil with the API symbol, this means the company has paid a license fee to the API, and in turn the API has tested its product to ensure it meets the applicable standard. If the API grades are simply listed on the bottle without the circular API symbol, this means the company claims to meet the API standards, but has decided not to obtain API licensing. This process is very expensive, and therefore many smaller producers choose not to be members, even though their products may be good enough to pass.
Every few years the API releases a new standard that is often specified by auto manufacturers, with the changes usually aimed at achieving lower levels of friction to obtain higher fuel economy, and to deal with other emissions-related issues. This is a never-ending battle in the automobile industry, as stricter federal emission and fuel economy standards are being imposed on automobiles. The API works with the auto industry to ensure that the oils are doing everything possible to reach these goals.
The motorcycle industry followed the ever-changing API service designations until a few years ago, when the SJ designation lowered maximum levels of certain additives used to reduce metal-to-metal friction. (The latest API designation is SL.) Specifically, the maximum allowable phosphorous content was lowered from 0.12 percent to 0.10 percent due to its negative effect on some catalytic converters. An engine burning oil will pass this phosphorous through the exhaust system, resulting in damage to oxygen sensors and catalytic converters. Since the EPA requires all emissions-related parts to be covered under warranty for seven years, this was a major motivator for manufacturers to meet the new standard.
Who is the JASO?
The motorcycle OEMs felt that lower levels of phosphorous and the introduction of more friction modifiers (aimed at higher fuel economy in cars) was not in the best interest of motorcycle engines. Since phosphorous is an important antiwear component, lower levels could reduce the ability of oil to protect transmission gears, since motorcycles share engine oil with the gearbox. Plus, added levels of friction modifiers could cause problems with slipping clutches, as well as less than optimal performance of back-torque limiting devices that lessens wheel lock-up on downshifts.
Rather than continue to rely on specifications dedicated to automobiles, the Japanese Automotive Standards Organization (or JASO) developed its own set of tests specifically for motorcycles. JASO now publishes these standards, and any oil company can label its products under this designation after passing the proper tests. JASO offers two levels of certification, MA (high friction applications) and MB (low friction applications). JASO requires that the entire product label be approved before it can carry its label. If a label does not have a box with a registration number above the MA or MB lettering, it could be nonapproved oil whose manufacturer claims its products meet JASO standards when it may not have actually passed the tests.
These standards also include a test specifically designed to measure the oil's effect on clutch lock-up, as well as heat stability and several other factors related to motorcycle engines. Our advice here is pretty simple: Read your manual, and if it calls for an API SG oil, use that. Don't substitute a higher API designation oil like SL, because it will contain less of some additives like phosphorus, and it may contain other additives that will yield higher fuel economy in a car but could cause slippage in your clutch. (More on that later.)
While it may not be the perfect answer, you can also be safe by selecting JASO-labeled oil, because you will know that it has passed a bank of tests developed by the motorcycle industry. A quick look in several 2002-'03 owner's manuals showed that an '03 Kawasaki ZX-12R and most Hondas were the only sportbikes in our shop carrying a mention of JASO.
What Are Base Stocks?
Motor oils start with a base oil mixed with various additives. These base oils often account for approximately 80 to 90 percent of the volume, and are therefore the backbone of oil. Everyone knows that some oils are petroleum-based and some synthetic, while others are labeled semi-synthetic. What does all this mean? Well, not as much as it used to, because the lines are now blurred in the case of synthetic oils.
For our purposes, petroleum oils are the most basic and least expensive oils on the market. They are created from refined crude oil and offer good properties, though they are generally not as heat resistant as semi-synthetics or full synthetics. On the other end of the spectrum are synthetic oils. A synthetic oil has been chemically reacted to create the desired properties. Semi-synthetics are a blend of the two base stocks.
The API groups oils into five major categories, each with different properties and production methods:
Group I: Solvent frozen mineral oil. This is the least processed of all oils on the market today and is typically used in nonautomotive applications, though some of it may find its way into low-cost motor oils.
Group II: Hydro-processed and refined mineral oil. This is the most common of all petroleum oils and is the standard component of most petroleum-based automotive and motorcycle engine oils.
Group III (now called synthetic): The oils start as standard Group I oils and are processed to remove impurities, resulting in a more heat-stable compound than possible as a standard Group I or II oil. Some examples are Castrol Syntec automotive oil and Motorex Top Speed. These are the lowest cost synthetics to produce, and generally do not perform as well as Group IV or V oils.
Group IV: Polyalphaolefin, commonly called PAOs. These are the most common of the full synthetic oils, and usually offer big improvements in heat and overall stability when compared to Group III oils. They are produced in mass quantities and are reasonably inexpensive for full-synthetic oils. Since they are wax-free they offer high viscosity indexes (low temperature pour point) and often require little or no viscosity modifiers. Examples include Amsoil and Motorex Power Synt.
Group V: Esters. These oils start their life as plant or animal bases called fatty acids. They are then converted via a chemical reaction into esters or diesters which are then used as base stocks. Esters are polar, which means they act like a magnet and actually cling to metals. This supposedly offers much better protection on metal-to-metal surfaces than conventional PAOs, which do not have this polar effect. These base stock oils also act as a good solvent inside the engine, translating into cleaner operation. Esters are the most expensive to produce, and oils manufactured with them usually cost much more. Due to this higher cost, many companies only fortify their oils with esters. Some examples are Bel-Ray EXS, Torco MPZ Synthetic and Maxum 4 Extra. Motul 300V, however, uses 100 percent ester as its base oil, and is one of the more expensive oils.
The grouping of these oils is the source of much controversy. One topic that has been debated is what can be labeled a "full synthetic oil." In 1999, Mobil brought a complaint against Castrol for changing the base oil in its Syntec product. They had used a Group IV PAO, but had changed to a Group III base oil. Mobil contended that Group III oils were not really "synthetic oil" and should not be labeled as such. After many expert opinions were heard, the National Advertising Division of the Better Business Bureau sided with Castrol and said that Group III oils could be labeled synthetic. Since that time there has been a lot of growth in this product type due to its low cost and similar performance to traditional synthetics. Many traditionalists still argue that Group III oils are not true synthetic oils.
Additives to the oil
Additives are the other 10 to 20 percent of the product that help the base oil do things that it otherwise could not. Additives fall into several basic categories:
Detergents/Dispersants: These ensure that foreign materials in the oil stay in suspension to allow the filtration system to remove dirt or debris.
Corrosion Inhibitors: These prevent oil from deteriorating from the attack of free radicals or oxidation.
Antiwear: These are perhaps the most- discussed additives, which serve to protect the engine from metal-to-metal wear. Common antiwear additives are phosphorous and zinc. Other antiwear additives include friction modifiers like molybdenum disulphide (or moly).
Acid Neutralizers: Additives like calcium, magnesium and boron act to absorb acids created during combustion to protect the engine. They are typically indicated by the TBN (Total Base Number). A higher number means the oil should last longer and provide increased protection against combustion-based acids.
Other additives such as foam inhibitors, viscosity modifiers and antirust components may also be present in motorcycle oils. In particular, antifoaming additives are important due to the high RPMs that can create cavitation and starve bearings from necessary lubrication in the process.
If you ask someone with years of riding under his belt what viscosity oil he uses, he may answer "20W-50." All multiviscosity oils carry two numbers. In simple terms, the first number is the oil's viscosity when cold (32Fahrenheit/0Celsius), and the other is the oil's viscosity at operating temperature (212F/100C); the "W" stands for "weight" or viscosity, which is simply the liquid's resistance to flow. In other words, when the oil is cold it will flow like a 20-weight, but when hot it will act like a 50-weight. In order to overcome the natural thinning that occurs as oil heats up, a component known as a viscosity modifier is added. This is a complex polymer that swells due to heat, the net result being that the oil thins less.
Typically, synthetic oil contains less of this additive, or in some cases none at all due to its naturally higher viscosity index. This is another reason why they are better suited for the wide range of temperatures and riding conditions associated with motor-cycle use. Viscosity modifiers are one of the first additives that wear out in oil, and a big reason that some synthetic oil manufacturers claim longer service life. Since they are naturally a multigrade product without the chemical modification mineral oils require, synthetic oils will hold their viscosity grade longer.
The reason the old-timer may suggest thicker oil is because in older engines with higher tolerances, thicker oils were necessary to keep oil pressure up. Others believe the use of higher viscosity oils results in better protection because high-performance engines are harder on oil. This isn't true in modern engines, and using oil thicker than specified can actually harm an engine. Internal oil passages and galleys may not be large enough to allow thicker oils to penetrate and flow as well, which can possibly cause starvation. In fact, many race teams use the thinnest oil possible to gain extra horsepower by lowering the parasitic losses that occur when using thicker-than-necessary oil. The higher film strength offered by synthetic base stocks helps racing engines survive even endurance races when running ultra-lightweight oils. Of course, these engines are typically rebuilt after each race, so we do not suggest using a racing oil in your streetbike. Refer to your owner's manual and use the viscosity of oil corresponding to your riding conditions as specified by the manufacturer. The manuals often have a table with various temperatures allowing you to select the right viscosity.
Can synthetic oils cause my clutch to slip?
To answer this in one word: No. Clutch slippage is caused by many things, but the use of synthetic oil alone is usually not the culprit. The truth is that some bikes seem to suffer clutch slippage no matter what oil goes in them, while others run fine with any oil. This is most likely caused by factors other than the oil, such as the spring pressure, age and clutch plate materials. If you have a bike known for clutch problems, you may have to be more selective in your oil choices. Moly is often blamed for clutch slippage, and it can have an effect-but moly alone is not the problem. We wish there was a hard and fast rule to follow, but it is just not that easy. Simply put, you will have to try an oil and evaluate it. If you experience slippage with the new oil, and have not had problems before, it may be the oil. The plates and/or springs could also be worn to the point that they have finally started to slip. Simply change back to the previous oil and see what happens. You can also check the test data in next issue's article to see if that particular oil has a significant amount of moly. If so, try one that does not have as much moly next time.
We talked to Mark Junge, Vesrah's Racing representative, who has won numerous WERA national championships using Vesrah's clutches. He said that in his years of engine work he has yet to see a slipping clutch that could be pinned on synthetic motor oil. Junge felt that nearly every time the clutch was marginal or had worn springs, the new oil just revealed a problem that already existed.
Stay tuned for Part Two: Analysis, Wear and Dyno tests
This is the first part in a two stage article, so please stay tuned to the next issue where we will reveal the test data from an analytical oil laboratory as well as the results of our dyno horsepower shootout, where we will have a face-off of two different products to see if changing oils can yield horsepower gains as some manufacturers claim.
This article originally appeared in the August, 2003 issue of Sport Rider.