|I am not a lubrication, filtering, chemical or mechanical engineer. I
have a degree in engineering, but I studied electrical engineering. I now
study physics. You may feel free to question my abilities to gather facts
and draw conclusions in the area of oils and filters. In any case, this is a
write up of what I learned in about 60 hours of research on this topic. My
only interest is having my motorcycle run forever, never break, and be easy
Why do we need oil?
Where Oil Comes From
The oil we pump to the surface is a mixture of gasoline, kerosene, light weight lubricating oil, motor oil, gear oil, tars, paraffins, waxes, asphalt, sand, dirt, organic stuff (called aromatics) and the occasional dead cockroach. We call this stuff crude oil, for reasons that I think are now self-explanitory. The oil companies have the singularly smelly job of separating the crude oil into its component parts. A hundred years ago we would just heat the stuff up in a complicated still, and catch stuff that boiled off at different temperatures. Fifty years ago we started processing the crude oil with clay and solvents to do a more precise job. Today, we use very complicated systems where we heat the crude oil to precise temperatures, put it under high pressure, and bubble hydrogen and other stuff through it. The idea of all this is to try to get pure chemicals out of this stuff that we just found laying around in the desert.
Most motor oil has a lot of different chemicals in it with very different properties. The temperature at which the oil will start burning, called the flash point, is determined by the chemicals that burn at the lowest temperature. The higher the flash point, the more stable the oil is at high temperatures, and the less oil your engine will burn. The pour point is the temperature at which the oil stops flowing like a liquid. The lower this number is, the better protected your engine is when it's cold. The thickness of the oil, that is the resistance the oil offers to motion, is called the viscosity. The viscosity depends on all of the various chemicals in the oil and how they react to each other and to heat. Importantly, as the oil heats up, it thins out, that is the viscosity goes down. The better the oil is at retaining its viscosity at high temperatures, the higher the viscosity index. All of these properties depend on all the chemicals in the oil. If you could get only one precise kind of molecule out of the raw oil, you could do a lot better than you can do with a mix.
Base oils that are refined from crude oil are colorless and pretty much odorless and are sold to the public as mineral oil. The curde oil is a combination of a lot of different chemicals, ranging from light gasolive types of fuels to waxes and tars. When you heat the crude oil, the gasolene and diesel oil boil off pretty early. Unfortunately, the mineral oil, paraffin, wax and tar molecules are all hooked up with each other, and it's not so easy to seperate them from each other. There are currently 5 classes of base oil, called Group I, II, III, IV, and V. Group I oil is refined the old-fashioned way using clay and solvents, and is used in about 2/3 of the oil sold in America today. Group I oils contain a fair amount of pariffin and wax. These molecules cause several problems in an engine: they sometimes fall out of solution, leading to buildups in your engine that must be cleaned out somehow. Also, as these molecules get hot they thin out quite a bit, much more than mineral oil, so they make the oil's high temperature performance rather poor.
In 1990, Chevron developed a new method of refining base oils called Hydrocracking, where you process the raw oil at high temperatures and pressures with hydrogen. In Hydrocracking, many of the pariffin and wax molecules are broken up into mineral oil molecules, which increases the performance of the base oil dramatically. Base oils made with this method are called Group II, and are significantly more pure and have higher performance than Group I base oils. Chevron Delo 400, Mobil Delvac 1300, and Shell Rotella are made from pure Group II oils. Motor oils made with hydrocracked base oils leave far fewer wax and tar deposits in your engine, and have much better high temperature performance than group I oils.
Since 1990, Chevron's process has been improved. By increasing the severity of the hydrocracking process, raising the temperature and pressure to break up more and more of the unwanted wax and pariffin molecules, the viscosity index (VI) can be improved further. The VI tells us how much the oil thins out as it gets hot. Oils with higher VIs maintain their viscosity better at high temperatures. If the VI is 90 to 100, we call it Group II; if it's refined to a VI of 110 to 115 we call it Group IIa. In the late '90s, an even more involved process was invented yielding base oils with VIs over 120. These base oils are called Group III or "unconventional base oils." The higher the VI, the fewer additives are necessary to achieve the required viscosity. For example fewer additives are needed to turn a Group III base oil into 10w-40 than are required for Group II base oils.
These Group III oils have properties approaching synthetics, so long as the temperature is above about 40°. Group III based oils are often claimed to not perform as well as synthetics in a couple ways: their low temperature performance is not nearly as good, it is sometimes claimed on the basis of the "ball bearing test" that they offer lower impact resistance, and since their flash point is slightly lower it is claimed that they burn off more easily. However, most modern engines are water-cooler, so it's hard to see how the slightly better flash points of the synthetics ever come into play. I personally don't make a habit of dropping a handful of ball bearing into my oil pan, so I'm not completely clear on what the impact tests mean to me. The low temperature performance of the Group III oils can be improved enormously by blending in a relatively small amount of synthetic base stock.
In the late 1990s, Castrol started selling an oil made from Group III base oil and called it SynTec Full Synthetic. Mobil sued Castrol, asserting that this oil was not synthetic, but simply a highly refined petroleum oil, and therefore it was false advertising to call it synthetic. In 1999, Mobil lost their lawsuit. It was decided that the word "synthetic" was a marketing term and referred to properties, not to production methods or ingredients. Castrol continues to make SynTec out of Group III base oils, that is highly purified oil with most all of the cockroach bits removed.
Shortly after Mobil lost their lawsuit, most oil companies started reformulating their synthetic oils to use Group III base stocks instead of PAOs or diester stocks as their primary component. Most of the "synthetic oil" you can buy today is actually mostly made of this highly-distilled and purified dino-juice called Group III oil. Group III base oils cost about half as much as the synthetics. By using a blend of mostly Group III oils and a smaller amount of "true" synthetics, the oil companies can produce a product that has nearly the same properties as the "true" synthetics, and nearly the same cost as the Group III oil. In fact, Mobil-1 is now primarily made from Group III unconventional base oils, exactly the stuff Mobil was claiming was not really synthetic. The much more expensive traditional synthetics are now available in their pure forms only in more expensive and harder to obtain oils.
One process for making synthetic base oils is to start with a chemical called an olefin, and make new molecules by attaching them to each other in long chains, hence "poly." The primary advantage of Poly-Alpha-Olefin "PAO" base oil is that all the molecules in the base oil are pretty much identical, so it's easy to get the base oil to behave exactly as you like. PAOs are called Group IV base oils.
Another type of base oil made from refined and processed esters and is called Group V. Esters start life as fatty acids in plants and animals, which are then chemically combined into esters and diesters. Group V base stocks are the most expensive of all to produce. However, the esters have very significant solvent properties - an ester base oil all by itself will do a very decent job of keeping your engine clean. So, people who are serious about making a superior oil will usually mix some Group V oils into their base stock.
Finally, there are new chemicals emerging which are made from liquefied natural gas called GTL (gas to liquid) base oils. These will perhaps be called Group VI, and many people think they will become an important part of the oils you buy within a few years. Natural gas is primarily made up of only one type of molecule, so the refining is already done for you. Most oil wells throw off a lot of natural gas. In many cases, it's more expensive to transport this gas to a large city than the gas is worth, so it's just burned off. For example, Iran burns off enough natural gas each day to power their entire country, electricity, cars, ships, airplanes, the whole thing. So the next time you hear Iran's nuclear reactors are purely for peaceful production of energy, you can wonder like the rest of us why a country that burns off more than their entire energy needs must spend tens of billions of dollars developing alternative energy sources. Well, anyway, natural gas is a chemical looking for a use. All you have to do is chemically attach these molecules to each other to turn them into quite pure oil stocks.
"Semi-synthetics" are oils which are a blend of petroleum oil and no more than 30% synthetic oil. If the manufacturer adds no more than 30% synthetic oil and does not change the additive package, they do not have to recertify the oil. These days, since everyone has agreed that Group III base oils are "synthetic," I'm not sure "semi-synthetic" means anything at all.
Making Multi-Grade Oil
An oil sold as 10w-40 is no thicker than 10 weight oil under Winter (10w) conditions, meaning at 32° Fahrenheit. The 40 means it is no thinner than 40 weight oil at 212° Fahrenheit. So, the first number tells us the performance of the oil at the temperature of freezing water, and the second number tells us the performance at the temperature of boiling water. The chemicals added to the oil to accomplish this are called Viscosity Index Improvers (VIIs).
To make a 10w-40 oil, the manufacturer would start out with a 10 weight oil as the base stock. All by itself, this oil would thin out so much at normal operating temperatures that the oil film would be useless. So, they add these very special very long molecules, the VIIs. The VII molecules are as much as 1000 times as long as an oil molecule. The VII molecules curl up in a little ball at room temperature, but as the temperature gets higher they uncurl and stretch out, like a cat sleeping in the sunlight. The more stretched out the molecule is, the more it impedes the normal flow of the oil, thus raising the effective viscosity. Now, this sounds just a little too good to be true. Well, there are two catches: first, these molecules are not lubricants, so the more of them that you add the less oil you have sitting around lubricating things. Secondly, these VII molecules can be broken into pieces by various pressures and forces, like being squeezed through the transmission gears in a motorcycle. Every time a VII molecule gets broken, the oil loses some of its high temperature viscosity. Synthetic oils made from pure PAOs and/or Diesters typically have very few VIIs, so these oils are far less subject to viscosity breakdown due to shearing of the VII package. As a result, synthetics are far more stable in a motorcycle engine.
10w-30 oil increases its viscosity at high temperatures by a factor of three, which requires a significant amount of these VII molecules. 10w-40 oil increases its high temperature viscosity by a factor of four, which requires even more even longer molecules. 20w-50, which sounds a lot like 10w-40, only increases its high temperature viscosity by a factor of two and a half, so it requires fewer of these molecules than even 10w-30. 15w-40 also increases its high temperature viscosity by about two and a half, so this oil is also substantially more stable than 10w-40. Most passenger car oils today use inexpensive VII molecules that break apart relatively easily. Conversely, most diesel engine oil VIIs are chosen from more expensive chemicals that are more shear stable, since an oil change in a large diesel is expected to last for 15,000 to 150,000 miles.
In 1994, Dr. John Woolum tested the viscosity of several 10w-40 oils in his motorcycle. He found that all of the petroleum oils had lost highly significant amounts of viscosity within 1500 miles. Only Mobil-1 held up in his test. I have personally tested Delvac-1 synthetic in my ST1300. It was 5w-40 when I put it in, and 5w-25 9,200 miles later. By 1500 miles, the petroleum oils Dr. Woolum tested were at 10w-25. By contrast, Dr. Woolum tested a petroleum oil in his Honda Accord. After 3600 miles, the 10w-40 oil was 10w-37. Motorcycles are indeed significantly harder on their oils than cars.
You might ask, if these viscosity index improvers are so expensive and fragile, why have them? Why not just run a straight 30 weight oil? If you live somewhere where the temperature never changes, like Maui, maybe that's a good idea. However, if your engine will ever see temperatures below 60 degrees or above 100 degrees, it's important to have a multi-weight oil. Multi-weight oils offer far superior protection during a cold engine start on a cold morning, and they also offer superior protection if your engine oil ever gets above about 230°. Of course, some old timers will tell you, "I always ran straight 50 weight oil. Yup. That was the stuff. All these new-fangled fancy oils, forget it, it's just marketing hype. All you need is straight 50 weight." Well, that may have been true when motorcycles were 1500ccs and made 18hp. Today, when you can casually buy an engine that makes 150hp per liter, things are just a little different.
Viscosity is not actually measured in "weights", but rather in units called "Stokes." If you're a famous scientist they name a unit after you, except for poor Albert who is considered famous enough all by himself. Stokes was a guy who worked on fluid flow. For oils, we use a hundredth of a Stoke, called a centi-Stoke, abbreviated cSt. "Weights" are a classification invented by the American Petroleum Institute (API). 10 weight oil refers to oils within a range of viscosities, so two different brands of 10 weight oil might actually be quite different. 75 weight gear oil is actually about the same viscosity as 10 weight motor oil. Don't ask me why, I'm not a petroleum engineer; although some might argue that I do belong in an institution.
Motor Oil Additive Packages
One component is detergents and dispersants. These chemicals are designed
to hold onto foreign particles and chemicals in your engine, and sometimes
break them into smaller pieces. These foreign chemicals may be combustion by
products, or junk that slipped past your air filter. If the particles are
large enough, then they will eventually be grabbed by the oil filter and
taken out of circulation.
The additive packages sold for C (commercial) certification are designed to promote engine life. The additive packages for C rated oils contain extra buffers and detergents to keep the engine clean and free of acids. Generally, C rated oils are far better than S oils at holding and dispersing combustion byproducts and other contaminants, and at not becoming acidic. Traditionally these oils are primarily used in diesel motors, which are very expensive and are expected to last a million miles or more. When an engine rebuild costs $10,000 - $15,000 and puts you out of work for a week or three, you don't mind paying a bit more for your oil. The C certification tests have been largely developed by Mack, Caterpillar, and Cummins to provide the additives necessary to keep these engines running a long time. The latest commercial certification is CI-4, which includes extra protection for high temperature high revving motors. Since it's designed for diesel motors, they don't care about no stinkin' catalytic thingys, and CAFE is a place where you get a cup of joe and a donut.
The C certified oils are all also S certified, just as some S certified oils are also C certified. The best C certified oils are SH, sometimes SJ. I don't know of a C certified oil which is SL. The best S certified oils are CF, which is a relatively old C standard, and does not include the tests for high speed high temperature engines that CG, CH, and CI have. In fact, CF oil does not meet the current factory standards for Volkswagen or Mercedes diesel passenger cars.
The API charges serious money to test an oil and certify it. If the API really tested the oil in their independent lab, and the oil company pays their royalties on time, the oil company gets to display the API seal on their product. Some smaller companies don't pay the API to test their oils and certify them. In these cases, you won't see the API seal, instead you'll see some words like "Meets or exceeds all manufacturers warranty requirements. API Service SJ, SL, CF." It's up to you to decide if you trust this manufacturer to actually test their oil themselves and tell you the truth about the results.
Another institute that certifies oils is called the Japanese Automotive Standards Organization, JASO. One wonders why this Japanese organization has an English name. . . In any case, they have two classifications for motorcycles, "MA" and "MB." MA is the one you want. MB is like the API SL category, it's got all those nasty friction reducing chemicals that may scare your clutch into misbehaving. Again, there is an official JASO seal if the oil has been independently tested. The seal is a rectangle; in the upper quarter of the rectangle will be a serial number, and the lower three quarters will just have the letters MA. If the oil manufacturer did their own testing, instead you'll see just words like "Meets or exceeds JASO MA standards."
Some manufacturers also sell something they call "racing oil." Normally, this is actually fairly decent oil, but you should not be mislead into thinking racing cars use the best oils for you. Race drivers start their engine one time only, warm it up slowly and carefully, then run the engine near or at the red line for a couple hours. 100 to 500 miles later, they completely tear down the engine and replace all the worn parts, the oil, and the oil filter. If you think you might like to go more than 500 miles between major engine rebuilds, you might consider that your use of your engine is quite different from Michael Andretti's.
Why do we change our oil?
Choosing an Oil for Your Motorcycle
Most motorcycles have wet clutches, which means the motor oil runs
through the clutch. If the motor oil has too much molybdenum in it, there
are fears that the clutch can start slipping. No one I know has ever
actually had this happen to them, but the warnings are all over your owners'
manual and the oil companies' web pages. On the back of all certified oil
cans is a circular stamp with the certification. Avoid oils that say "energy
conserving" in the bottom half of the donut. These oils contain friction
modifier additives that could cause clutch slipping over time. Essentially
all 10w-30 oils are energy conserving, and should not be used in your
Synthetic oils have a higher viscosity index than mineral base oils.
Synthetics have better resistance to thinning at high temperatures and
thickening at low temperatures.
Some people should, in my opinion, clearly use a synthetic oil. You should be using a synthetic if you routinely start your engine in temperatures under 40°f, 5°c. You should use a synthetic if you leave your motorcycle sit unused for months at a time. You should use a synthetic if you are unable or unwilling to change your oil within 3000 miles. If you have one of these new 4-stroke MX bikes you should be running a synthetic. Some of these MX bikes hold only one quart of oil, all of them have marginal cooling systems, and if there's a more severe use of an engine than MX, I don't want to be physically present when it happens.
It seems pretty clear that if you change your oil every 2500 miles or so and never miss, you can use pretty much anything. If you want to go the full Honda 8,000 mile recommended service life or more, I believe you must use a synthetic. It would be nice to have hard evidence on the viscosity and acidity of different oils as they are run for many miles, but at this time almost no such evidence exists. Current measuring devices cost about $1500 for the portable versions, or you could send samples of your oil off to a lab at about $50 per sample. Perhaps sometime someone will produce a relatively inexpensive portable instrument, then we could change our oil when it was used up instead of relying on some kind of educated guess from averaged data.
Two synthetics stand out from the rest: Mobil Delvac 1 and Shell Rotella T Synthetic. These are C certified industrial oils meant to be purchased in 55 gallon drums and used by companies which run a lot of diesel engines. The Commercial oils, as discussed above, have more expensive additive packages which are meant to prolong engine life and oil life, as opposed to being cheap to buy at Pep Boys and helping the car companies meet their CAFE requirements. These oils meet all the automobile requirements through SJ, and also have extra additives to help pick up gunk in the engine, to keep the oil from becoming acidic, and to maintain the oil's viscosity over a long time. In fact, the manufacturers talk about their oil's viscosity resistance to shear forces - exactly what a motorcycle needs. Shell Rotella-T Synthetic is available at Wal-Mart for $13 / gallon, so I consider this the motor oil of choice. Delvac-1 is very hard to get in the west - there are only two places in all of California where you can buy it. When used with the correct filters, these oils are certified for 50,000 mile oil change intervals, and are frequently used for 100,000 to 150,000 miles in diesel long-haul trucks. Now, before you get all excited about the possibilities, you must also keep in mind that the diesel engines don't run their oil through their transmission, and the large diesels all have two oil filters, one a normal paper filter, and the other a 1 or 2 micron filter that catches pretty much everything. We don't have these secondary ultra-fine oil filters on our bikes. Also, the large diesel engines hold eleven gallons of oil - a oil and filter change costs these guys $350 if they use synthetics, $150 if they don't.
The synthetic diesel oils are 5w-40 oils. Some people have expressed concern to me that this doesn't match the 10w-40 specification for their engine. The 5w rating only applies when the oil is cold, below about 80° f. Once your oil and engine are up to operating temperature, these are 40 weight oils, just like all the others. In cold conditions, under 40° f, the 5w oils are much better for your engine than a 10w oil.
AMSOil, Motul, Mobil-1 MX4T and Golden Spectro are apparently made with high quality additive packages, similar to the commercial synthetics. Personally, I would find it reassuring if these oils were CI-4 certified. However, many motorcyclists have used these oils for years with good results. They are all fine oils, and perfectly acceptable to run in your motorcycle.They are a bit on the pricey side. AMSOil and Motul synthetics contain no petroleum oils - they're pure synthetic. To the best of my knowledge, all other synthetic oils contain some amount of Group III oil.
Mobil-1 Red Cap is a fine oil. It does not have the commercial additive package that Delvac-1 has, so I don't consider it as good an oil, but it's a perfectly acceptable oil to use in your bike. The Green, Blue, and Black Cap Mobil-1 oils are all energy conserving, and should not be used in your motorcycle.
If you live in another country, you'll have to do a bit of research to decide on an oil. Generally, any oil certified for use in a late model Volkswagon or Mercedes turbo diesel is a good choice. Another good idea is to go to a truck stop and ask the truckers about brands. Rotella is marketed all over the world, but in other countries it's called Rotella or Rimola or Helix Ultra, and the formulation may be a bit different, depending on local climate and preferences. It will likely also be a lot more expensive than it is here.
If you prefer a less expensive petroleum oil, Chevron Delo 400, Mobil Delvac 1300, and Shell Rotella T are available at any auto parts store for under $7 per gallon. This price is reasonably competitive with passenger car oils, and you are getting a Group II oil with the superior commercial additive packages. I don't have any information about how long you can run these oils before their viscosity breaks down, but I'm confident it's at least as long as the best consumer petroleum oil. If you're really into saving money, you can often find these oils locally in 10 gallon drums for about $50. This should keep your bike, your car, and your wife's car in good shape for at least a year. Farmers, ranchers and truckers buy these oils in large quantities, and we get to ride piggy-back on their economies of scale.
If you want to do some research on oils yourself, here are some links. I read all this stuff and I'm still alive, but a bit weird. Oil viscosity defined. API Service classifications. Everything you ever wanted to know about oil, but were afraid to ask. Here's what an additive package manufacturer has to say about oils. Lubricants primer by Red Line. All about oil by Ed Hackett, a college professor. Oil Advice from Mike Guillory, a petroleum engineer. More Oil Advice. Jeff Di Carlo also has an opinion. Check out the articles in MCN Jan-Feb '03. MCN '94 includes viscosity breakdown testing. The history of synthetic oils, only *slightly* self- serving. Oil additives = snake oil? (yes)
Mobil wants your money, as does Shell, Valvoline, AMSOil and Spectro Oil. You may be skeptical about the oil companies interests, but they are the people making what we buy so it's interesting to hear who they think we are and what they think we need.