How to Choose Between Synthetic and Conventional Motor Oil

Premium Conventional Oil: This is the standard new-car oil. All leading brands have these oils, which are available in several viscosities and tested under the latest API service level. Automakers usually specify a 5W-20 or 5W-30 oil for colder temperatures, with a 10W-30 oil as optional for higher ambient temperatures. These three ratings cover most light-duty vehicles on the road. Even more important, though, is changing the oil and filter regularly. We recommend changing your oil every 4,000 miles or four months. The absolute minimum is twice a year. If your car has an electronic oil-change indicator on its instrument cluster, follow its guidance instead and be sure to reset it once your oil change is done.

Full Synthetic Oil: Oils made for high-tech engines or heavy-duty uses, be it a Ford F-150 that tows frequently or a Chevrolet Corvette with the latest supercharged LS engine, are full of synthetic additives. These oils’ labels indicate whether they’ve passed stringent special tests for superior, longer-lasting performance in all the critical areas, from viscosity index to protection against deposits. They flow better at low temperatures and maintain peak viscosity at high temperatures. So, why shouldn't everyone use them? These oils are expensive and not every engine needs them. There may even be some features that your engine needs that synthetic oils don't have. Again, follow the guidance in your owner's manual.

Synthetic Blend Oil:
These have a dose of synthetic oil mixed with organic oil, and are formulated to provide protection for somewhat heavier engine loads and high temperatures. This generally means they're less volatile, so they evaporate far less, which reduces oil loss and increases fuel economy. These oils are popular with drivers of pickups or SUVs who want extra protection for activities that put more stress on the engine, such as hauling heavy loads. They're also much less expensive than full synthetics—sometimes just pennies more than a premium conventional oil.

Higher-Mileage Oil: Today's vehicles simply last longer. If you prefer to pay off your car and run the mileage well into the six figures, you have another oil choice:, oils formulated for higher-mileage vehicles. Almost two-thirds of the vehicles on the road have more than 75,000 miles on the odometer. Consequently, oil companies identified this as an area of customer interest, and have new oils they're recommending for these vehicles.

When your vehicle is somewhat older and has considerably more mileage, you may notice a few oil stains on the garage floor. Engine seals such as those around the crankshaft may have hardened and lost their flexibility, so they leak and may crack, especially at lower temperatures. You’ll need to check your oil levels more frequently and may need to top off your oil between oil changes.

Higher-mileage oils are formulated with conditioners that flow into the pores of the engine seals to restore their shape and increase their flexibility. Most rubber seals are designed to swell just enough to stop leaks, and oil refiners pick their "reswelling" ingredients carefully. Valvoline showed us the performance data of one of their seal conditioners that caused most seal materials to swell while reducing the swelling of one seal material that tended to expand too much from the ingredients found in some other engine oils.

You also may have noticed some loss of performance and engine smoothness due to engine wear on your higher-mileage vehicle. These higher-mileage oils also have somewhat higher viscosities. Even if the numbers on the container don't indicate it, there's a fairly wide range for each viscosity rating and the higher-mileage oils sit at the top of each range. They may also have additives to improve their viscosity index. The result? They seal your pistons better against their cylinder walls and won't leak as much through larger engine bearing clearances that have worn down with time. They also may have a higher dose of antiwear additives to try to slow that wear process.

If you have an older vehicle, these features may mean more to you than what you might get from a full synthetic at a fraction the price.

Going Deeper

What is metalworking fluids & their advantages


An oil’s resistance to thinning in hotter temperatures is called the viscosity index. Although a higher second number is good, the oil also has to be robust, lasting for thousands of miles until the next oil change. Oil tends to lose viscosity from shear, which is the sliding motion in the tight clearances between metal surfaces,such as those found in bearings. So, resistance to viscosity loss—called shear stability—is necessary to enable the oil to maintain the lubricating film between those parts.

Unlike antifreeze, 95 percent of which is made up of one base chemical (typically ethylene glycol), petroleum-based engine oil contains a mixture of several different types of base oils—some of which are more expensive than others. Oil companies typically pick from a selection of five groups, each of which is produced in a different way and in different viscosities. The more expensive groups are more highly processed, in some cases with methods that produce a lubricant that can be classified as a synthetic. The so-called full synthetics contain chemicals that may be derived from petroleum but are so altered that they're not considered natural oil anymore. For example, one custom blend contained 10 percent polyalphaolefins (PAO), which is the most common type of chemical used as the primary ingredient in a full synthetic oil.

The base oil package in any oil makes up anywhere from 70 to 95 percent of the mix; and the rest is composed of additives. An oil with just 70 percent base oils isn’t necessarily better than one with 95 percent base oils. Some base oils have natural characteristics or ones that derive from their processing, which reduce or eliminate the need for additives. Although some additives make improvements lubrication, they don't necessarily have great lubricity on their own.

The ingredients in an additive package differ in cost, but price is just one factor. Some additives work better in certain combinations of base oils. Likewise, some less expensive base oils are a good choice for a blend because of the way they perform with popular additives. Bottom line: Every motor oil has a recipe. Refiners come up with a list of objectives based on the needs of their customers (including the carmakers themselves) and formulate oils to meet those goals as best they can.

Keeping an oil from thinning as it gets hot while it takes a beating from engine operation is one thing, but it's also important to keep oil from becoming too thick. Using less volatile premium base oils to prevent evaporation is one approach. Evaporation of the base oil package not only increases oil consumption—it results in thicker oil, which decreases fuel economy.

Oil Additives

Oil companies’ use of additives is another approach to improving and maintaining oil performance. High engine temperatures combine with moisture, combustion byproducts (such as unburned gasoline), rust, corrosion, engine-wear particles and oxygen to produce sludge and varnish, which can gum up and damage the engine. Additives help maintain good lubrication by minimizing sludge and varnish. Here are the main categories of additive ingredients and why they're important:

• Viscosity-index improvers: These reduce the oil's tendency to thin with increasing temperature.
• Detergents: Unlike the kind you use to wash clothes, detergents in oil don't scrub engine surfaces. They do remove some deposits—primarily solids. However, their main purpose is to keep surfaces clean by inhibiting the formation of high-temperature deposits, rust, and corrosion.

• Dispersants: These disperse solid particles by keeping them in a solution so they don't come together to form sludge, varnish or acids. Some additives work both as detergents and dispersants.

• Antiwear agents: Sometimes the lubricating film created by oil breaks down, so antiwear agents have to protect the metal surfaces. A zinc and phosphorus compound called ZDDP is a long-used favorite, along with other phosphorus (and sulphur) compounds. If you must know, ZDDP stands for zinc dialkyl dithiophosphate.

• Friction modifiers: These aren't the same as antiwear agents. They reduce engine friction and thus, can improve fuel economy. Graphite, molybdenum and other compounds are used for this.

• Pour-point depressants: Just because a 0 degrees Fahrenheit viscosity rating is low doesn't mean that oil will flow readily at low temperatures. Oil contains wax particles that can congeal and reduce flow, so these additives are used to keep it flowing in the cold.

Antioxidants: With tighter emissions regulations resulting in higher engine temperatures, antioxidants are needed to prevent oxidation that thickens the oil. Some of the additives that perform other functions also serve this purpose, such as the antiwear agents.

• Foam inhibitors: The crankshaft whipping through the oil in the oil pan causes oil to foam. Oil foam is not as effective a lubricant as a liquid stream, so oils have foam inhibitors that cause the foam bubbles to collapse.

• Rust or corrosion inhibitors: These protect metal parts from acids and moisture.

More Is Not Better

You can't necessarily improve an oil by putting in more additives. In fact, you can make things worse. For example, sulphur compounds have antiwear and antioxidation characteristics, but they can reduce fuel economy and reduce the effectiveness of your catalytic converter. Too much of a specific dispersant can affect catalyst performance and reduce fuel economy. Antiwear and friction-reducing additives also may have ingredients that could affect catalyst performance, such as sulphur, which companies are being pressured to use less. Adding tToo much of some detergents can also affect antiwear characteristics.

Don't Forget the Filter

Oil filters are a completely different,albeit related, subject when it comes to changing your oil. Again, it's always best to consult your owner’s manual for the type of filter required. Some aftermarket filters are larger, so make sure you have some extra oil if you use one.

Post time: Feb-21-2022