“If your $20-per-quart synthetic looks dirty on the dipstick, you’d better change it now, ’cause all mechanics say dirty oil will ruin the engine. It’s science!”
“Speaking of, were you on the forums today? There’s an oil thread—yeah, another one—about how Europe gets way better synthetic oils than we do. Yeah, German cars get a Group 69 ultra-hyper synthetic made from plants harvested at the summit of the Zugspitze, and we Americans have to get by with sludge-filled dino oil. You believe that nonsense?”
“Whatever. I’m gonna change mine at 500 miles to be safe, then throw in three bottles of additives, ‘cause the zinc’ll turn my LS7 into an L88.”
How many times have you heard some variation of these oil “tips”? There’s the timeless “change it every (insert comically low mileage interval here)” advice. And the always popular “for the love of God and Team America, never let a drop of non-synthetic touch your oil pan” gem. Our guess is, you’ve heard ’em lots of times. We have too, and believed more than a few of them. Why is that?
Because like many other high-tech products today, motor oils are extremely difficult to understand—and unlike a smartphone, you can’t just take oil apart. You can ogle the port work on a new set of heads and read their dyno results, or fondle the strong shaft of a billet shifter (as this is a lubrication article, we’ll stop right there). But trying to understand oil quality is like trying to figure out Walter White: you have no clue about what’s going on in there, and can only hope that it’s not going to blow something up.
Complicating matters further, when the GF-4 oil standard came out awhile back, it drastically reduced the zinc and phosphorus used in oil for anti-wear protection. While newer, roller-valvetrain Vettes from later C4s to C7s aren’t affected, it’s a serious concern for owners of earlier, flat-tappet-valvetrain models.
Yes, we Corvette fans ask lots of questions about oil. So VETTE asked a few oil experts to help us explain it: The geniuses at Mobil 1, Driven Racing Oil, and Brad Penn assisted us right-brain types in getting our heads around this intimidating topic so you could as well.
We won’t pull punches: This tech goes deep. But once you have a general understanding of motor oil, you’ll realize just how much cutting-edge technology lives in that quart bottle. Let’s get started.
Once you have a general understanding of motor oil, you’ll realize just how much cutting-edge technology lives in that quart bottle.
The Refining Process
Crude oil contains thousands of compounds. Thanks to refineries, companies are able to use different refining processes that turn crude oil into everyday items such as lubricating oils, fuels, plastics, and waxes.
How Crude Oil is Refined
Three major refinery processes—separation, conversion, and purification—turn crude oil into finished products.
Separation is a distillation process that uses a series of separation (or distillation) towers and heat to physically separate crude oil into its naturally occurring components.
In the separation towers, a furnace heats and vaporizes the crude oil. The vapor/liquid mix is fed into the bottom of the tower, where temps can reach 750 degrees (F). Components that are still liquid at those high temps become the tower’s bottom product. Components in vapor form rise up through a series of distillation stages. As the temps decrease, the components condense and end up in their predetermined spots. So the heavy stuff like “bottoms” (which becomes asphalt base) stays on the bottom, mid-weight stuff like gas oil and diesel distillate (which become gasoline and diesel) goes in the middle, and lightweight stuff like “light ends” (which becomes propane) goes to the top.
But gas oil and diesel distillate doesn’t just “become” the gasoline and diesel that we pump into our vehicles. That’s where conversion comes in.
Conversion processes take low-demand products like heavy oil and rearrange the molecules into high-demand products like gasoline. This is possible because all of the products in the refinery are based on hydrocarbons with carbon and hydrogen chains.
Special units called fluidized catalytic crackers (FCCs), cokers, and hydrocrackers are used to “cut” the heavy oil’s longer carbon chains into shorter chains, which converts heavier hydrocarbons into lighter ones like gasoline. Additionally, there are catalytic reformer and alkylation conversion processes that can put these chains together, and even change the form of the chains.
Other conversion processes include delayed cokers, which convert the heaviest vacuum tower components into other products, and catalytic reforming, which increases the octane number of gasoline blends.
The purification stage physically cleans unwanted substances out of the product. This is done by hydrotreating, a process that puts the product in contact with hydrogen, then uses heat and high pressure in the presence of a catalyst. The result is hydrogen sulfide—and desulfurized product. While sulphur is the main target, aromatic hydrocarbons and paraffin wax are removed too.
How Lube Distillates Become Base Oil
Now let’s narrow down the refining process to lubricants:
After crude oil passes through the separation towers, it’s sent to cracking units to break up the hydrocarbons’ long carbon chains. This creates a group of carbon compounds that have between 25 and 45 carbon atoms, called lube distillates.
Next comes processing, where solvent extraction, dewaxing, or hydrotreating is used:
- Solvent extraction is a conventional process that removes aromatics.
- Dewaxing is either a conventional solvent process or a catalytic chemical process that removes long-chain, high-melting paraffins.
- Hydrotreating is a hydrogen treatment that removes carbon-to-carbon double bonds in aromatics and unsaturated paraffinics.
The processing methods can vary, depending on the required quality of the finished base oil. For instance, a solvent extraction method is used for Group I oils, and a more advanced hydrocracking method is used for Group II and III oils.
Base oils that are more highly processed have a higher purity, a higher group number, higher performance, and, usually, a higher cost. We’ll have more on oil base-stock group numbers in a bit.
Oil Base Stocks and Additives
Carbon and hydrogen molecules known as hydrocarbons make up the foundation of mineral oils. Different types of hydrocarbon molecules have different characteristics, and some types are more desirable for creating motor oil than others.
The foundations of synthetic oils vary: Some are chemically altered mineral oils, while others are esters or polyalphaolefins.
Let’s separate these molecules into two groups—mineral base oils and synthetic base oils—and discuss their different characteristics.
Mineral Base Stocks
There are three main groups of mineral base oil:
The first are paraffinics, which may be further divided into two subgroups: normal paraffinics and iso-paraffinics.
Normal paraffinics are straight-chain hydrocarbons. Because they are waxy, iso-paraffinics are typically preferred. The latter contain side chains that improve the viscosity index. They also have better oxidation stability, all of which has earned them a reputation as being the best mineral lubricants.
Naphthenics have the characteristic of naphthenes—saturated hydrocarbons with molecules containing at least one closed ring of carbon atoms. Similar to ring compounds like aromatics (but lacking double bonds), naphthenics are considered better than aromatics, but inferior to paraffinics.
Aromatics are unsaturated molecules with one or more benzene rings. Because aromatics are undesirable for motor oils, they’re normally extracted, and only trace amounts are left after refining.
Synthetic Base Stocks
There are several main groups of synthetic base oil used in automotive applications:
Polyalphaolefins (PAOs) are branched-chain, isoparaffinic hydrocarbons known as synthetic hydrocarbons. They’re similar to mineral hydrocarbons, but instead of being extracted like mineral oils, PAOs are manmade using a chemical process. The result is purer, uniformly sized molecules that are completely saturated—they have high oxidative and thermal stability, a high viscosity index, and a very low pour point. They’re also superior in extremely hot or cold temperatures. This highly versatile base stock is great as high-performance motor oil, and superior to mineral oil. The only downsides are a low solubility (which results in poor additive compatibility) and a high price.
Esters like diesters and polyol esters are branched synthetic hydrocarbons that are structurally similar to PAOs. The difference lies in an ester’s hydrocarbon molecules, which contain oxygen in the form of ester linkages. These linkages polarize the molecules, which results in esters having a higher flash point and lower volatility compared with PAOs. The polarity also helps esters “stick” to the engine’s metal surfaces, which gives them additional film strength and lower energy consumption. They’re also great detergents, more environmentally friendly, and they’re very flexible so engineers can build a specific oil for specific applications. Downsides are that esters can affect the elastomer material used in engine seals, and they can react if they come into contact with water. While esters were some of the first synthetic automotive oils, they’ve been surpassed by PAOs due to a PAO’s lower cost and ease of formulation.
Through advanced chemical processes, the new Group III+ base oils (which we’ll discuss shortly) can now be considered a “synthetic.”
As defined by the American Petroleum Institute (API), a base stock is “a lubricant component that is produced by a single manufacturer to the same specifications (independent of feed source or manufacturer’s location); that meets the same manufacturer’s specification; and that is identified by a unique formula, product identification number, or both.”
Base stocks are divided into five categories, or groups: Group I, Group II, Group III, Group IV, and Group V. Through a specific test method, each group has a different makeup of saturates, sulfur percentages, and viscosity index.
Group I: Base stocks that contain less than 90 percent saturates and/or greater than 0.03 percent sulphur, and have a viscosity index greater than or equal to 80 and less than 120.
Group II: Base stocks that contain greater than or equal to 90 percent saturates and less than or equal to 0.03 percent sulphur, and have a viscosity index greater than or equal to 80 and less than 120.
Group III: Base stocks that contain greater than or equal to 90 percent saturates and less than or equal to 0.03 percent sulphur, and have a viscosity index greater than or equal to 120.
Group IV: Base stocks are polyalphaolefins (PAO) with no unsaturated hydrocarbons or sulfur. PAOs may be interchanged without additional qualification testing, as long as the interchange PAO meets the original PAO manufacturer’s specs in physical and chemical properties.
The following key properties need to be met in the substituted stock:
1. Kinematic viscosity at 100, 40, and -40 degrees (C)
2. Viscosity index
3. Noack rating (volatility)
4. Pour point
Group V: Base stocks that include all other base stocks not included in Group I, II, III, or IV. Group Vs like esters are typically used for creating oil additives.
Group III+ Base Stocks
While not currently included in the base-stock groups, III+ base stocks bridge the gap between the highly refined mineral Group III base stocks and the expensive, synthetic Group IV base stocks. They provide performance that’s above what normal mineral oils can give, yet they’re more affordable than the Group IV synthetics—and as you can imagine, they’re very popular these days. ExxonMobil’s Visom is an example of a Group III+ base stock.
Oil Additive Packages
Motor oil is made by combining base oil with a complex mixture of up to 15 additives. Generally speaking, there are two types of fluids that make up an additive package: a detergent-inhibitor package, and a viscosity-index improver.
The detergent inhibitor (or DI) package is a mixture of performance additives that’s needed for an oil formulation.
- Anti-foams are non-soluble silicone molecules that help prevent oil from foaming, and also help disperse foam that’s already formed.
- Antioxidants like amines and phenolics help fight oxidation, a reactive process that can create carbon deposits in an engine.
- Detergents are metals and organic chemicals that clean engine deposits and neutralize acid byproducts from combustion. Common metal atoms used include calcium, magnesium, and sodium; common organic products include salicylates, sulfonates, and phenates.
- Diluent oil, or carrier oil, is a mineral oil that helps the solubility of the additives, and ensures that the viscosity is in the correct range for pumping and blending.
- Dispersants suspend and disperse the solid pieces left over from the combustion of fuel. As those pieces would otherwise end up as engine sludge, dispersants are kind of a big deal. Not surprisingly, they’re one of the main components of a DI pack.
- Friction modifiers are molecules that, thanks to their polarity, attach to an engine’s metal surfaces to improve lubricity. They can also improve fuel economy. Organic friction modifiers are typically esters or glycerol mono-oleates (GMO). Inorganic Friction modifiers are molybdenum compounds.
- Pour-point depressants keep the trace amounts of paraffins in oil from growing crystals. PPDs aren’t usually needed in PAO- and ester-based oils, as they don’t contain wax.
- Rust/corrosion inhibitors attach to, and protect, engine metals like iron from acid-, oxygen-, and water-based corrosion.
- Seal conditioners are esters that keep seals pliable. They are especially needed in Group III and Group IV oils, which are known to shrink and harden seals.
- Zinc dialkyldithiophosphate (ZDDP) has been used for years as an affordable anti-wear, extreme-pressure, antioxidant additive. ZDDP is also the most well-known additive, as it is both erroneously vilified for ruining catalytic converters and O2 sensors, and celebrated for keeping flat-tappet engines alive. We’ll discuss ZDDP in more detail in the Additives section.
Viscosity-index improvers, as their name implies, improve a finished oil’s viscosity index. The key to VIIs is their large polymeric molecules: They coil up when cold, which makes little difference to the oil’s viscosity. But when hot, VIIs uncoil and stretch out, which reduces oil thinning—and increases the oil’s viscosity. That improved viscosity index allows manufacturers to create multi-viscosity oils.
Oil Viscosity, Weights, Properties, and Standards
At this point, you should have a basic understanding of how crude oil is refined into base stock, then combined with additives to create motor oil.
If your head hasn’t exploded at this point, relax—the hard part’s over. Now, let’s discuss some of the more hands-on aspects of motor oil: oil weights, single- and multi-grade oils, and industry standards.
When discussing the weight of a motor oil, we think of its “thickness.” But we’re really discussing viscosity. There are many different measurements and classifications for lubricant viscosity, and this topic gets complex in a hurry. But the core concept is pretty easy to understand.
Viscosity is defined as a physical measurement of a lubricant’s internal resistance to flow. Let’s use water and honey as examples: Water, which flows easily, has a low viscosity. Honey, which doesn’t flow easily, has a high viscosity.
There are several conditions that affect the viscosity of a lubricant in an engine: they include temperature, speed, and load.
The temperature of an engine’s operation changes the viscosity of a lubricant. Generally, when the temp goes up, viscosity goes down, and when the temp goes down, viscosity goes up.
The speed of an engine’s operation affects what viscosities can be used. The lubricant will need to flow well at high speeds, but it can’t be too thin at lower speeds or it won’t lubricate correctly.
The load of an engine’s operation also affects what viscosities can be used. Heavy loads can compress the lubricant film, so a higher viscosity may be needed to prevent damage. However, if the engine only sees normal load conditions, a lower viscosity may be adequate—and with less resistance, it can result in better fuel economy as well.
To determine the proper viscosity for your engine, you’ll need to account for its operating temperature and environment, rpm range, and types of loads experienced. The right viscosity should provide an adequate lubrication film at both high and low temperatures. It should also flow well at both high and low temps and operating speeds, and possess a film strength that stands up to light and extreme operating loads. If that seems like a tall order, it is.
Standard Oil-Testing Methods
Because today’s vehicles and ever-tightening regulations keep asking more of motor oils, manufacturers must continually improve their oils to meet that challenge. And that’s where advanced test methods come in. There are numerous oil-testing methods conducted by organizations such as ASTM International and SAE, as well as the oil manufacturers themselves. Here are a few examples of these tests:
The base number test measures a lubricant’s reserve alkalinity, which helps control acids created during the combustion process.
The flash point test determines the temp at which oil gives off vapors that can be ignited with a flame. As you can imagine, the higher the flash point, the better.
The pour point test finds the lowest temp at which the oil will flow, using a specific test method and measured in degrees F. The lower the pour point, the better.
The shear stability test measures how much viscosity oil loses during operation. After its viscosity is measured, oil is run through extreme shearing conditions. The viscosity is measured after testing, and the difference between the pre- and post-test oil viscosities determines the percentage of viscosity lost.
Viscosity tests measure the time it takes a lubricant to flow by gravity. Some viscosity tests include low-temperature cranking viscosity, low-temp pumping viscosity, and high-temp kinematic viscosity.
The viscosity index is a number that shows oil’s relative change of viscosity over a temp range. The higher the VI, the smaller the viscosity change over temperature, which is better.
Simple terms like “30 weight” come from the complex SAE J300 standard, which is a viscosity classification for engine oils. It classifies viscosity grades based on low-temp tests such as low-temp cranking viscosity and low-temp pumping viscosity, and high-temp tests such as kinematic viscosity at 100 degrees (C).
For example, a 0W viscosity grade has a 3.8 kinematic viscosity at 100 degrees, while a 50 viscosity grade has a 16.3 kinematic viscosity at the same temp. Or, simplified, the 0W is thin, while the 50 is thick.
Engine-oil weights are as follows:
- “W” (winter) weights: 0W, 5W, 10W, 15W, 20W, 25W
- Standard weights: 16 (new), 20, 30, 40, 50, 60
Multi-Grade vs. Single-Grade Oil
In the early days, all cars used single-grade oils. However, today’s street vehicles overwhelmingly use multi-grades. Single-grade oils can still found in everything from racing cars to lawn tractors, but this type accounts for only a small portion of overall motor-oil production.
Multi-grade (or multi-viscosity) oils like 5W-30 use viscosity-index improvers (VIIs) that allow the oil to perform well in nearly all temperature ranges: A 5W-30 multi-grade oil provides the cold cranking protection of a 5W and the high temperature viscosity of a 30-weight oil in one—that is, it’s thin enough to flow in low-temp situations like cold startups, yet thick enough to protect in high-temp situations like extended high-rpm driving. Multi-grades also provide incremental fuel-economy savings over single-grade oils.
Single-grade (or single-viscosity) oils like 30 weight are just that, a single viscosity. They don’t use VIIs and, as such, aren’t recommended in certain climates (cold winters in the northeast, for example). While it used to be said that in favorable summer weather, a single-grade oil could provide better engine-bearing protection than a multi-grade, today’s advanced multi-grade oils provide much better protection and a much greater operating-temp range.
Note that a multi-grade oil is almost always the smart choice for your street-driven Corvette.
The American Petroleum Institute (API) is a trade association that grades motor oils. The institute’s starburst graphic, which can be found on most quarts of oil, advertises that the oil meets the current engine-protection standard and fuel-economy requirements of ILSAC (more on that anon). API uses a two-letter service category designation that denotes the current performance standard.
ILSAC, the International Lubricants Standardization and Approval Committee, is a trade organization that works with vehicle manufacturers and commercial engine-oil producers, and is responsible for creating passenger-car engine-oil specifications. The API and ILSAC have worked cooperatively for years, and their ratings track on a parallel path. ILSAC uses a three-digit alphanumeric service-category designation that denotes the current performance standard.
Current API/ILSAC Oil Standards
- API: SN (2010-up)
- ILSAC: GF-5 (2010-up)
(Note that the API also has an oil standard for diesel engines; the current, 2007-up standard is CJ-4.)
API’s SN standard was introduced in October 2010, and provides improved high-temp deposit protection for pistons, more-stringent sludge control, and seal compatibility. API SN with Resource Conserving matches ILSAC GF-5 by combining API SN performance with improved fuel economy, turbocharger protection, emission-control-system compatibility, and protection of engines operating on ethanol- containing fuels up to E85.
ILSAC’s GF-5 standard was also introduced in October 2010, and provides improved high-temp deposit protection for pistons and turbochargers, more-stringent sludge control, improved fuel economy, enhanced emission-control-system compatibility, seal compatibility, and protection of engines operating on ethanol-containing fuels up to E85.
Previous Oil Standards
- API: SJ (1996-older), SL (2001-older), SM (2004-older)
- ILSAC: NA (all previous standards obsolete)
Obsolete Oil Standards
- API: SA, SB, SC, SD, SE, SF, SG, SH
- ILSAC: GF-1, GF-2, GF-3, GF-4
Decoding an Oil Container
Many people have no idea how to read a quart of oil. Thankfully, API’s starburst and ILSAC’s “donut” make choosing the latest oil-standard spec easy.
The API starburst is usually found on the front of the bottle and reads, “AMERICAN PETROLEUM INSTITUTE CERTIFIED FOR GASOLINE ENGINES.”
The ILSAC donut is usually found on the back of the bottle. We’ll use the current standard on a quart of 5W-30 oil: “API SERVICE SN SAE 5W-30 RESOURCE CONSERVING.”
The bottle may also show previous API specs that the oil also covers, as well as manufacturer specs such as “GM 6094M” and “GM 4718M.”
Picking up a name-brand offering with the current performance standards on the bottle is the best way to choose a quality oil. But look closely: On a recent trip to a big-box store, we found Mobil 1 Extended Performance “gold” 5-quart containers with the new SN standard, but the Mobil 1 “blue” 5-quart containers only had the SL standard.
Additives, Specialty Oils, and Flat-Tappet Protection
Since the beginning of the automobile and up to the early 1970s, drivers relied on mineral oil to protect their engines. Then came synthetics, with their superior protection qualities (and a few shortcomings, like making engine seals shrink). The oil companies learned from early mistakes, and made synthetics more user friendly. Today, oil engineers can spend their entire careers on developing new additive packages. Why is that important? Read on.
You may be aware that many older engines used flat-tappet cams. And pre-1990s oils had high (1,000-plus ppm) levels of zinc and phosphorus (specifically, zinc dialkyldithiophosphates, or ZDDP), which provided the protection those flat-tappet engines needed.
But in the ’90s, ZDDP levels were reduced in an effort to better protect oxygen sensors and catalytic converters. The auto industry had largely moved to roller cams anyway, so the 800 parts-per-million limit of ZDDP worked fine with newer engines.
However, those ’90s oils’ ZDDP levels were too low to protect flat-tappet engines, and as the tales of engine wear appeared, the aftermarket exploded with ZDDP additives.
To this day there’s a dedicated additive following out there, and some enthusiasts even use diesel-specific oils in an attempt to better protect their valuable engines. But according to the experts we consulted, you shouldn’t use those additives (or diesel oils) in your Corvette.
Why? Oil is a delicate mixture, and adding ZDDP or other substances to your oil can upset that mix. For that reason, in most cases, running additives does more harm (in the form of wear) than good.
If you’re concerned about protecting your Corvette’s flat-tappet engine, or just want a bit more protection for your late-model C4-C7, you have a few options:
1. Use Mobil 1’s 15-50. This heavier-weight oil offers increased ZDDP content, added film strength, and better high-temp protection. And even though it has around 1,200 ppm phosphorus and 1,300 ppm zinc, it’s still API certified, as this viscosity isn’t required to have the lower ZDDP level.
2. Use a “street/’strip” oil like Brad Penn Grade 1. Brad Penn, while not a household name, has a great reputation for producing quality oils. Pennsylvania-grade crude oil is known for high-quality base stocks and great film strengths. Grade 1 adds high ZDDP concentrations that, while not recommended for late-model vehicles, is said to provide outstanding protection for flat-tappet and roller engines alike. (Late-model owners should try Brad Penn’s FSGF synthetic, an API SN-level oil with excellent anti-wear properties and catalytic-converter/oxygen-sensor friendliness.)
3. Use an oil specifically for your engine type, like Driven Racing Oil’s LS30 synthetic for ’97-up LS-powered Corvettes. These high-tech mills have unique issues: lifters ticking during startup, PCV blow-by, roller-cam lobe wear, and lifter and bearing failure. Driven claims that LS30 provides optimum oil flow on startup, which eliminates lifter ticking. It also features a high-temp, high-shear blend that can withstand an LS’s high-temp, high-rpm environment. Its low volatility prevents PCV issues and oil consumption, and the high zinc content protects aggressive roller cams. LS30 can even keep the variable valve-timing system running smoothly in VVT engines like the ’14 Vette’s LT1. 3.
While new-vehicle owners can just take it easy for 500 miles then change the oil, engine builders must break in each new mill carefully. And break-in oils are carefully formulated with the right viscosity to seat the rings, as well as the right anti-wear additives that protect the cam and valvetrain, and minimize damaging metal particles created during break-in.
Flat-tappet-engine builders are typically conscientious about using a proper, high-ZDDP break-in oil like Brad Penn Grade 1 30-weight to protect internal components. However, some roller-motor owners mistakenly believe that their engines don’t need break-in oil. In reality, without a purpose-specific lubricant like Driven BR Break-In Oil, those roller mills will suffer the same particulate contamination—and potential bearing failures—that a flat-tappet engine would. So you ’87-up Corvette owners, take heed: If you’re rebuilding your roller Vette engine, break it in right!
Racing oils are different from street oils, because the engines and operating environments are different.
Modern street engines typically operate in low-rpm, low-load environments, and many are overhead-cam designs—all of which requires fewer anti-wear additives. A large emphasis is placed on emissions, so the engines use EGRs and other emissions equipment, and require additional detergents. And because of ever-increasing drain intervals, additional acid neutralizers are necessary.
Race engines operate in high-rpm, high-temp environments, and many use flat-tappet cams and pushrods—which need more anti-wear additives and friction modifiers. Emissions controls typically aren’t used, so there’s less need for detergents. Racing oils are generally lower in viscosity (though many are still multi-viscosity types, like street oils), but have zinc, phosphorus, and moly levels beneficial for anti-wear protection. However, they’re designed for low-mileage use, with drain intervals usually before 500 miles.
Dexos and the ’14 Stingray
You may have heard about GM’s new oil called dexos1. Developed specifically for GM gasoline engines, dexos1 is the factory-fill oil in vehicles like the Cadillac ATS and the ’14 Stingray.
Some characteristics of the dexos1 synthetic-blend oil:
- Improved viscometric properties, for less friction in the engine and improved fuel economy
- Resists aeration, which enables fuel-saving devices, such as variable valve timing, to work optimally
- Reduces oxidation and deposits, allowing emission systems to operate longer and optimally
- Resists degradation between oil changes, extending the time and mileage interval between oil changes
You can use GM’s dexos1, or you can choose to use one of the GM-licensed dexos1 products found at www.centerforqa.com/gm/dexos1-brands.
Mineral vs. Synthetic: Which is Better?
Ah, the age-old “Should I use synthetic or mineral oil?” question.
Mineral oils should be used in special situations: Driving an ancient car, breaking in a new engine because your builder says it seats the rings better, etc.
Outside of that, you should always use a high-quality synthetic or synthetic-blend oil in your Corvette. And it doesn’t matter if your ride used conventional oil until now; switching to synthetic won’t cause any problems.
Today, we’re fortunate to enjoy the most advanced oil formulations ever made. Modern synthetics and synthetic blends provide superior protection, even when extending drain intervals to 7,500 miles in some GM vehicles.
They’re better at preventing engine wear, their purity and detergents keep the engine internals cleaner, and they control combustion- related acids better. They flow much faster in cold temps, and they don’t break down and form deposits in high-temp environments. They cool and seal better than ever before. Some have additive packages that can go 15,000 miles, and many even contribute to improved fuel economy. That, my friends, is called progress.
What used to be a hotly debated topic has turned into a no-brainer: Today’s synthetic oil technology makes it vastly superior to mineral oil, period.
Corvette Oil FAQ with Mobil 1
Most Corvette owners are familiar with Mobil 1 synthetic oil. The Corvette-Mobil 1 partnership started in the early ’90s, when GM approached ExxonMobil about creating a lubricant that performed at high temps. ExxonMobil responded by creating a high-temperature performance specification based around the performance capabilities of Mobil 1 synthetic oil. Mobil 1 became Corvette’s factory-fill oil in 1992, and it went on to be used in such ultra-high-performance Vettes as the ZR1, Z06, and Grand Sport.
U.S. Motorsports Technical Advisor Roger Hood discusses Mobil 1 oils with Corvette owners at track days. We asked him what kinds of oil questions he hears from Corvette owners, and here’s what he said:
VETTE Magazine: Why did Mobil 1 take zinc out of their oils?
Roger Hood: This is the most-asked question I hear at seminars. Zinc and phosphorus- compound content is a huge topic with guys who own older Vettes with flat tappet [engines]. In short, roller valvetrain technology didn’t need as much zinc, and phosphorus levels were damaging cat converters, so the levels were reduced in the GF-4 oil standard.
For older Vettes, we recommend Mobil 1 15W-50 street oil for its higher zinc content. And for Corvettes with no cats, or track-only Corvettes, we recommend 0-50 Mobil 1 racing oil.
VM: Can I add additives like ZDDP to Mobil 1?
RH: We don’t recommend any extra oil additives, as it could upset the delicate balance of the additive package. You may cause engine wear or other problems if you add additives!
VM: What oil should I run at track days?
RH: We know that Corvette owners spend a lot of money on these cars, and are concerned about high temps on tracks like VIR, etc.
For Corvette owners who want to put their cars on track, we recommend draining out the 5W-30 and replacing it with 15W-50 street oil. Some late-model owner’s manuals actually specify the 15W-50; it gives a stronger oil-film strength and higher temp protection.
VM: Should I still change my oil at 3,000 miles?
RH: I think the U.S. still has an identity crisis with the 3,000-mile oil-change mentality. Europe is way ahead of us there, like with BMWs having 15,000-mile oil change intervals.
People don’t understand the strengths of synthetic oils: the quality of their base stocks and additives. When you use Mobil 1, you can go longer between oil changes, and oil still stays in good shape and still protects your engine. These longer drain intervals are less expensive, and there’s a green aspect, too.
VM: Is Mobil 1 the same formulation, regardless of where I buy it?
RH: Regardless of if it’s a high-end store or a discount retailer, it’s the same Mobil 1.