How to choose the right engine oil?

With so many motor oil options available, selecting the right oil for your car may appear to be a daunting task. While there is a wealth of information available about the various oil options, the first step is actually quite simple: Examine the owner’s manual for your vehicle.

The recommended oil weight for your vehicle will be listed in the owner’s manual, whether it’s a standard format like 10W-30 or something more unusual. That figure represents the viscosity (or thickness) of the oil you should use. As mentioned below, you should change the weight and kind of the car based on the season and how you want to use it. What is listed in your owner’s manual is sufficient for regular use in moderate temperatures. Always buy oil from a brand that has the starburst symbol, which indicates that the oil has been tested by the American Petroleum Institute (API).

On the container, you’ll also notice a two-character service designation. The most recent API service standards are SP for gasoline engines and CK-4 for diesel engines. These letters are based on a series of laboratory and engine tests that determine the oil’s ability to protect the engine from wear, high-temperature deposits and sludge, and other contaminants. If you’re interested, the API has a complete list of these standards here, but make sure you’re buying oil that has been tested to the most recent standard. As of this writing, these are SP, SN, SM, SL, and SJ for gasoline engines, and CK-4, CJ-4, CI-4, CH-4, and FA-4 for diesels.

That’s the gist of the narrative, but there’s a lot more to it than that.

Understand the Labels

These are the labels you’ll find on every quality motor oil container. The API doughnut on the right indicates whether or not the oil is currently service rated. It also shows you if the oil has passed the Resource Conserving test and gives you the SAE (Society of Automotive Engineers) viscosity number. The left-hand starburst symbol denotes that the oil has passed the servicing tests stated in the other doughnut.


The resistance to flow of a fluid is referred to as viscosity. The viscosity of most motor oils is measured at zero degrees Fahrenheit (represented by the number preceding the W, which stands for winter) and at 212 degrees Fahrenheit (represented by the number preceding the W, which stands for summer) (represented by the second number after the dash in the viscosity designation).

As motor oil heats up, it becomes thinner and runnier, and as it cools, it thickens. Thicker oil, within reason, maintains a superior film of lubrication between moving parts and seals crucial engine components better. An oil can be rated for one viscosity while cold and another viscosity when hot with the correct additives to assist it avoid thinning too much in the heat. The higher the second number (10W-40 versus 10W-30, for example) is, the more resistant the oil is to thinning, which is a positive thing.

Meanwhile, oil must be resistant to excessive thickening in low temperatures so that it can reach all of your engine’s moving parts. Excessive thickness might make starting the engine more difficult, lowering fuel economy. The engine needs more energy to turn the crankshaft, which is partially buried in oil, if the oil is excessively thick. For cold-weather performance, a lower number before the W is better, therefore a 5W oil is often recommended for winter use. Synthetic oils, on the other hand, can be made to flow even more smoothly when cold, allowing them to pass 0W testing.

The oil heats up once the engine is going, which is why a higher second number is critical for demanding applications and hotter-running, more sophisticated engines.

Why Are There So Many Oils?

Oils designated for high-tech engines, new automobiles, higher-mileage vehicles, heavy-duty/off-road SUVs, and even cars from specific nations can be found in auto parts stores. You will find a wide range of viscosities.

You can find out what oil the vehicle’s manufacturer advised when it was new if you read your owner’s handbook. A mention to Energy Conserving or Resource Conserving oils may appear in the manual, indicating that the oil passed a fuel economy lab test against a reference oil. While this does not always equate to improved fuel economy, most major brands designate at least some viscosities as such.

How to Select Between Synthetic and Conventional Motor Oil

Premium Conventional Oil:

This is the standard oil for new cars. These oils are available in a variety of viscosities and have been tested to the most recent API service level. Automakers generally specify a 5W-20 or 5W-30 oil for colder temperatures, with a 10W-30 oil as optional for higher ambient temperatures. These three classifications apply to the majority of light-duty cars on the road. However, replacing the oil and filter on a regular basis is even more crucial. Oil should be changed every 4,000 miles or four months. A minimum of twice a year is required. If your car’s instrument cluster has an electronic oil-change indication, follow its instructions instead, making sure to reset it once your oil change is completed.

Full Synthetic Oil

Synthetic additives abound in oils designed for high-tech engines or heavy-duty applications, whether it’s a Ford F-150 that tows frequently or a Chevrolet Corvette with the latest supercharged LS engine. These oils’ labels indicate if they’ve passed rigorous special tests for greater, longer-lasting performance across the board, from viscosity index to deposit resistance. At low temperatures, they flow better and maintain peak viscosity at high temperatures. So, why should they not be used by everyone? These lubricants are costly, and they aren’t required for all engines. There may even be some properties that synthetic oils lack that your engine requires. Follow the instructions in your owner’s manual once again.

Synthetic Blend Oil:

These are developed to provide protection for slightly larger engine loads and high temperatures, and contain a blend of synthetic and organic oils. This implies they’re less volatile, which means they evaporate less, resulting in reduced oil loss and higher fuel economy. Drivers of pickup trucks or SUVs that want extra protection for activities that put more stress on the engine, such as transporting big weights, prefer these lubricants. They’re also less expensive than full synthetics, costing only a few pence more than a quality traditional oil.

Higher-Mileage Oil:

Vehicles today simply last longer. You have another oil option if you choose to pay off your automobile and drive it long into the six figures: oils developed for higher-mileage autos. Almost two-thirds of all automobiles on the road have travelled more than 75,000 miles. As a result, oil firms have noticed this as an area of client interest and are recommending new lubricants for these vehicles.

You may notice a few oil spots on the garage floor if your vehicle is a little older and has a lot more miles on it. Seals around the crankshaft, for example, may have stiffened and lost their flexibility, causing them to leak and shatter, especially at low temperatures. You’ll have to check your oil levels more frequently, and you might have to top off your oil in between oil changes.

Oils with higher mileage are prepared with conditioners that seep into the pores of the engine seals to help them regain their shape and flexibility. The majority of rubber seals are intended to expand just enough to stop leaks, and oil refiners carefully select their “reswelling” ingredients. Valvoline demonstrated the performance data of one of their seal conditioners, which caused most seal materials to swell while minimizing the swelling of one seal material that tended to expand excessively due to chemicals contained in other engine oils.

Taking it a Step Further

The viscosity index measures an oil’s resistance to thinning at higher temperatures. Although a higher second number is desirable, the oil must also be durable, lasting thousands of kilometres before needing to be changed. Shear, which is the sliding action in narrow clearances between metal surfaces, such as those found in bearings, causes oil to lose viscosity. Shear stability, or resistance to viscosity loss, is required for the oil to maintain the lubricating coating between those parts.

Unlike antifreeze, which is made up of 95 percent of a single base chemical (usually ethylene glycol), petroleum-based engine oil is made up of a variety of base oils, some of which are more expensive than others. Oil firms normally choose from one of five categories, each of which is manufactured differently and has varying viscosities. The more expensive groups are treated more thoroughly, in some circumstances using technologies that result in a synthetic lubricant. The so-called full synthetics are made up of chemicals that are sourced from petroleum but have been altered to the point that they are no longer considered natural oil.

In any oil, the base oil package makes from 70 to 95 percent of the blend, with the balance made up of additives. An oil with only 70% base oils isn’t necessarily superior than one with 95% base oils. Some base oils have natural properties or processing features that decrease or eliminate the need for additions. Although some additives help with lubrication, they don’t always have a high level of lubricity on their own.

The cost of the ingredients in an additive package varies, although price is only one consideration. Some additives function better with certain base oil combinations. Similarly, because of how they interact with common additions, some less expensive base oils are an excellent choice for a blend. In the end, every motor oil has a formula. Refiners create a list of goals based on the needs of their clients (which includes carmakers) and produce oils to match those goals as best they can.

It’s one thing to keep oil from thinning when it heats up and takes a hammering from engine use, but it’s equally crucial to protect oil from becoming too thick. One method is to use less volatile premium base oils to prevent evaporation. Evaporation of the base oil package increases not only oil consumption, but also results in thicker oil, which reduces fuel economy.

Oil Additives

The usage of additives by oil firms is another way to improve and sustain oil performance. Sludge and varnish are formed when high engine temperatures, moisture, combustion byproducts (such as unburned gasoline), rust, corrosion, engine-wear particles, and oxygen mix to form sludge and varnish, which can clog and damage the engine. By reducing sludge and varnish, additives aid in the maintenance of proper lubrication. The following are the most common types of additive components and why they’re important:

  • Improvers of viscosity index: These minimise the oil’s tendency to thin as the temperature rises.
  • Detergents: Unlike detergents used in the laundry, detergents used in oil do not scour engine surfaces. They do get rid of some residues, mostly solids. However, their primary function is to prevent the formation of high-temperature deposits, rust, and corrosion on surfaces.
  • 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 compounds are used to prevent metal surfaces from wear when the lubricating layer generated by oil breaks down. ZDDP, a zinc and phosphorus combination, has long been a popular choice, as have other phosphorus (and sulphur) compounds. ZDDP stands for zinc dialkyl dithiophosphate, in case you didn’t know.
  • Antiwear agents are not the same as friction modifiers. They can enhance fuel economy by reducing engine friction. This is done with graphite, molybdenum, and other chemicals.
  • Pour-point depressants: Just because an oil’s viscosity rating is low at 0 degrees Fahrenheit doesn’t mean it will flow freely at that temperature. These additives are used to keep oil flowing in the cold since it includes wax particles that can congeal and impede flow.
  • Antioxidants are essential to prevent oxidation, which thickens the oil, as a result of tougher emissions rules resulting in greater engine temperatures. Some additives, such as antiwear agents, that perform other tasks also serve this purpose.
  • Foam inhibitors: Oil foams due to the crankshaft whipping across it in the oil pan. Because oil foam is not as effective as a liquid stream as a lubricant, oils contain foam inhibitors, which force the foam bubbles to collapse.
  • Inhibitors of rust and corrosion protect metal parts from acids and moisture.

More Is Not Better

Adding extra additives to an oil will not necessarily improve it. In fact, you may aggravate the situation. Sulphur compounds, for example, offer antiwear and antioxidation properties, but they also compromise fuel economy and catalytic converter performance. Excessive amounts of a particular dispersant can degrade catalyst function and lower fuel economy. Antiwear and friction-reducing additives may also contain substances like sulphur, which firms are being encouraged to use less of. Some detergents’ antiwear properties can be harmed by using too much of them.

Don’t Forget the Filter

When it comes to changing your oil, oil filters are an entirely other, albeit connected, topic. Again, the type of filter necessary should always be determined by consulting your owner’s manual. If you utilise an aftermarket filter, make sure you have some additional oil on hand.

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