We delve into the super slippery realm of synthetic motor oils
—courtesy, Corvette Enthusiast magazine
Motor oil is the lifeblood that keeps your Corvette's engine running, literally. Without oil, the engine would seize and lock-up in a matter of minutes, if that long. While the primary purpose of motor oil is to lubricate and protect, it also functions to keep your engine cool and running clean.
There are basically three kinds of motor oil in use today: conventional motor oil refined from crude oil (petroleum) that is drilled from wells in the ground, synthetic or man-made oils that are formulated in laboratories, and blends of petroleum and synthetic oil. Petroleum motor oil had been the standard lubricant since the internal combustion engine first appeared; a couple of decades ago, synthetic oils appeared on the scene and have steadily gained favor. There are several reasons for this. Synthetic oils offer superior protection from engine wear; they have lower volatility (the tendency of oil to break down at extreme temperatures) for decreased oil consumption; they promote better gas mileage and easier start-ups at very cold temperatures, to name a few.
Petroleum oil is drilled from wells in the ground or under the ocean floor. Along with the oil come other undesirable components including sulfur, sulfur compounds, reactive hydrocarbons and other materials that cannot be completely removed during the refining process. These impurities cause sludge and cause the lubricating oil to break down in the engine over time.
Corvettes have been using Mobil 1 5W30 synthetic oil as the factory fill since 1992. According to Dave McLellan, the Corvette's second chief engineer, "The most important reason was that the LT1 engine needed an oil cooler for certain high thermal stress situations. We were concerned that the external oil cooler plumbing, which ran near the exhaust manifold, was vulnerable to manifold heat. Tests with Mobil 1 showed that the engine ran cool enough that an external oil cooler was not even needed." McLellan also added, "Corvette also used synthetics in Showroom Stock endurance racing for their power steering, manual transmission and axle."
It's a popular misconception that synthetic motor oils are designed to extend the time period between oil changes almost indefinitely, but in reality this isn't the case. While synthetics do provide additional protection above and beyond petroleum motor oils (see the sidebar), no lubricants last indefinitely; they get dirty and have to be changed at the intervals prescribed by the manufacturer. And, you should change the filter when you change your synthetic oil just as you would do with petroleum motor oil. Most synthetic oil manufacturers, however, claim that you can at least double the interval of your oil changes. (Even if you do go double or more on the interval of the oil changes, I'd still change the filter every 3K miles and top-off as necessary.)
Material Approx. Viscosity
Water at 70 degrees Fahrenheit 1
SAE 10 Motor Oil or Corn Oil 50-100
SAE 30 Motor Oil or Maple Syrup 150-200
SAE 40 Motor Oil or Castor Oil 250-500
SAE 60 Motor Oil or Glycerin 1,000-2,000
Corn Syrup or Honey 2,000-3,000
Blackstrap Molasses 5,000-10,000
Peanut Butter 150,000-250,000
Calking Compound 5 Million to 10 Million
Window Putty 100 Million
Viscosity refers to the thickness of a fluid.
This table illustrates the relative viscosity of numerous common fluids for comparison purposes.
What Makes It Synthetic?
Synthetic oils are considerably more expensive than petroleum motor oil because of how they are made. The name "synthetic oil" means that it is chemically synthesized from different hydrocarbons. The manufacturing process starts with a hydrocarbon, derives the gas ethylene and then chemically synthesizes that into the base stock for synthetic oil, polyalphaolefin (PAO). PAOs are extremely slippery man-made polymer chemicals with molecular strength and lubrication characteristics unsurpassed by any other lubricating fluid.
CAN YOU PICK UP PONIES JUST BY CHANGING YOUR OIL?
Virtually every synthetic oil manufacturer boasts that its product is the best, that it will give you extra power, increase mileage, last almost forever, etc. Royal Purple synthetic oil claims to be the "performance oil that outperforms." The company also boasts that their synthetic oil will measurably increase horsepower and torque. In a world filled with exaggerated claims and advertising hype, we decided to put Royal Purple's claims to the test.
I gave SLP Performance Parts in Toms River, New Jersey, a call, explained what I wanted to do and arranged to get some time reserved on their chassis dynamometer. The plan was simple and straightforward: We'd run a couple of dyno passes on a 1998 Corvette with a fresh fill of Mobil 1, drain it and fill it with Royal Purple using a new filter and run a couple of dyno passes to see if there was any difference in the hp or torque output. Brian Reese, SLP's director of engineering, suggested that we do the oil change with the C5 still harnessed on the dyno to virtually eliminate the chance for any variation due to harness tension between tests. With that, the C5 was tethered and the first dyno tests began. A second dyno pass was run to check for consistency of results and the second test result overlaid the first one exactly. The oil temperature was 200° when the tests were run.
The Mobil 1 was drained and the C5 filled with Royal Purple 5W30 with a new K & N filter. Two dyno passes were run after letting the Royal Purple warm up to 200°. Lo and behold, Royal Purple lived up to its claim as you can see from the actual dynamometer printout here. The actual dyno test numbers were as follows:
Oil SAE Power (HP) SAE Torque (Lb-Ft)
Mobil 1 344.5 358.0
Royal Purple 348.3 362.8
Total Gains 3.8 4.8
Formulated with appropriate additives, these polymer lubricants have been used for many years in such high-demand applications as aircraft jet engines, where oil changes between engine rebuilds are virtually unheard of. Polymer lubricants are also used in industries where machinery shutdown or interruptions to production to do oil changes would be cost-prohibitive. High-grade true polymer lubricants that have been used for these purposes are very expensive, in some cases as much as $50 per liter. Their high cost has made them prohibitive for everyday transportation use.
It is because of this high cost that many synthetic oils claiming to use PAOs in reality use only a very small amount of them, and this is primarily a marketing tool. They actually use less-expensive esters, additives, petroleum oil carriers or a blend of these for the balance of their product. Such oils are blends rather than true synthetics — an important distinction to understand. Premium additives that are beneficial for reducing friction, resisting oxidation and thermal breakdown and eliminating sludge and varnish formation all add to the cost as well. On the plus side, doubling the interval between oil changes helps to offset the increased cost to a large extent for the end consumer.
Because the oil is synthesized under controlled laboratory conditions, the molecules of the base stock of synthetic oil are all the same — their size is uniform and there are no impurities. This makes synthetic oil more stable and enables it to lubricate better. Additionally, due to the uniform size of the molecules, synthetic oil is less volatile under extreme heat and, if you freeze the oil, it will still pour when petroleum oil is solid.
Conversely, synthetic motor oil is created in a laboratory from special synthesized materials to deliver more lubricity, longer life and performance benefits.
Conversely, petroleum oil molecules are different sizes and shapes, some of which are undesirable. Owing to the fact that it is pumped from the ground, there are several impurities in crude oil such as sulfur, sulfur compounds, reactive hydrocarbons and other materials which can't be completely removed in the refining process, leaving them to end up in the final product. The viscosity (thickness) and lubricating qualities of the oil will change over time as the smaller molecules burn off and this also causes acids and sludge to form in petroleum motor oil.
The molecules of the synthesized hydrocarbon (left), which is the primary element of synthetic oil, are all uniform in size and free of foreign matter. The petroleum oil molecules (right) contain contaminants which can't be completely removed during the refinery process.
FULL SYNTHETIC VS. SYNTHETIC BLENDS
Many synthetic motor oils today are blends made with an ester base and contain petroleum oils as a carrier. These oils typically contain 70 to 85 percent synthetic esters by volume, with the balance being additives that are dispersed in the petroleum carrier oil. Semi-synthetics contain only about 10 to 15 percent synthetic esters as a base stock.
An ounce of prevention is worth a pound of cure, as the saying goes. A magnetic drain plug and an oil filter magnet will give you some added insurance against foreign metal particles circulating around the interior passages of your motor. Well worth the few dollars they cost for the added protection — and peace of mind.
The problem with ester-based oils is that they still contain petroleum and suffer from the same problems that pure petroleum oil does: They start to break down at high temperatures and relatively low mileage (about 5,000 miles at the outside).
True synthetic oil, on the other hand, contains no naturally occurring substances and doesn't need to be thinned out with additives and detergents before it can be used in a vehicle. In fact, the oil actually works as a natural detergent to clean out old engine deposits that may be remnants from petroleum oil used previously in the motor.
True synthetics don't break down at high temperatures and cause oxidation, nor do they cause sludge and block passages. Synthetics have a very low (below -40° F) pour point which make them ideal for use in extreme low-temperature conditions.
Myths & Misconceptions About Synthetic Oil:
3 MONTHS OR 3,000 MILES — WHICHEVER COMES FIRST?
The 3 month / 3,000 mile rule had been the accepted law of the land for decades while petroleum-based motor oils ruled, but things are quite a bit different with today's synthetic motor oils. Owner's manuals have been recommending much longer oil changes for several years and now there are oils that are guaranteed to be up to the challenge.
Virtually every manufacturer of synthetic oil states that you can get larger (sometimes incredibly larger) intervals between your oil changes without voiding your manufacturer's warranty. Some brands such as Exxon Mobil's high-endurance line of synthetics permit you to go 5,000, 7,500 or even 15,000 miles between oil changes by adding more cleaning agents into the various blends. Amsoil, the first manufacturer of fully synthetic motor oil, has customers who boast 60,000 miles (!) between changes. And MotrLube, hailing from Canada, also claims you can rack up thousands upon thousands of miles between changes, as do all the other major manufacturers.
While it is clear that synthetic oils do indeed provide superior lubrication and long-term protection above and beyond what even the best of petroleum-based oils can deliver, let your common sense be a guiding factor in deciding how long you want to go before oil changes. The most important thing to remember is that you can't do any harm by changing your oil and filter more often than is actually needed.
True or False: Synthetic motor oils damage seals.
False. Think about this for a minute: it wouldn't make too much sense for lubricant manufacturers to make products that are incompatible with seals, would it? Made from elastomers, seals are inherently difficult to standardize and it is the additives in the oil that affect seals. The additive mix is what controls seal swell, shrinkage and hardening regardless of whether it's a synthetic or petroleum product that is being produced.
True or False: Synthetics are too thin to stay in the engine.
False. In order for a lubricant to be classified in any SAE grade (5W30, 10W30, 10W40 etc.) it has to meet certain guidelines with regard to viscosity. For instance, regardless of whether it's 10W-40 petroleum or 10W-40 synthetic, at -25°C (-13°F) and 100°C (212°F) the oil has to maintain a standardized viscosity or it can't be rated a 10W-40.
True or False: Synthetics cause engines to use more oil.
False. Synthetic motor oils are intended for use in mechanically sound engines that don't leak and in such engines oil consumption will actually be reduced for three reasons: first, because of the lower volatility of synlubes; second, because of the better sealing characteristics between piston rings and cylinder walls; and third, because of the superior oxidation stability (i.e., resistance of synthetics against reacting with oxygen at high temperatures).
True or False: Synthetic lubricants are not compatible with petroleum.
False. The synthesized hydrocarbons, polyalphaolefins and other materials that form the base stocks of high-quality name-brand synthetics are fully compatible with petroleum oils. In the old days, some companies used untested ingredients that were not compatible, causing quality synlubes to suffer a bum rap. Fortunately those days are long gone. In fact, many of the leading synthetic blends are formulations of both synthetic and petroleum components.
Compatibility is something to keep in mind whether using petroleum oils or synthetics. It is usually best to use the same oil for topping off that you have been running in the engine. That is, it is preferable to not mix your oils even if it is Mobil 1 or Royal Purple you are using. The reason is this: The functions of additives blended for specific characteristics can be offset when oils with different additive packages are put together. For optimal performance, it is better to use the same oil throughout.
True or False: Synthetics void warranties.
False. No major auto manufacturer specifically bans the use of synthetic lubricants. In fact, increasing numbers of high-performance cars are arriving on showroom floors with synthetic motor oils as the factory fill.
New vehicle warranties are based upon the use of oils meeting specific API Service Classifications and synthetic lubricants that meet current API Service requirements are perfectly suited for use in any vehicle without affecting the validity of the new car warranty.
True or False: Synthetics last indefinitely.
False again. Nothing lasts forever. Although some experts feel that synthetic base stocks themselves can be used forever, it is a known fact that eventually the additives will falter and cause the oil to require changing. Moisture, fuel dilution and acids (the by-products of combustion) tend to use up the additives in oil, allowing degradation to occur. You can, however, replenish these additives by 'topping off'. Through good filtration and periodic oil analysis, synthetic engine oils protect an engine for lengths of time far beyond the capability of nonsynthetics.
THE BOTTOM LINE: If you have a 1992 or later Corvette, using synthetic oil is a given. If you have an earlier Vette, the choice of whether to stay with petroleum-based oil or to switch to a synthetic blend or pure synthetic is a decision you'll have to make for yourself. But now that you know the facts about synthetic oils, hopefully you'll be able to make a more informed decision. Regardless of what kind of oil you're using in your Corvette, the most important thing is to keep it clean and change it (and the filter) regularly. That's the best way to ensure you'll have thousands of carefree miles with your Corvette.
—courtesy, Corvette Enthusiast magazine