Regular Vs Synthetic Vs Semi-Synthetic Oil [Explained]

When it comes to choosing the right engine oil for your car’s engine, you’re spoiled for choices. The terms regular oil, synthetic blend, and fully synthetic oils are always thrown around at you. And that can lead to a lot of confusion. You may want to go for a synthetic oil but what if it’s an overkill and a waste?

You need to understand the differences between these oil types at a root level so that you can make the correct choice for your engine. That’s exactly what I’ll break down in this regular vs synthetic vs semi-synthetic oil guide for you.

Starting from the manufacturing to the components to the differences in oil types, all your questions will be answered in this guide. So, let’s dive right into the world of engine oils!

regular vs synthetic vs semi-synthetic oil

Regular Vs Synthetic Vs Semi-Synthetic Oil [Explained]

You need to understand the manufacturing process and the composition of each oil to understand their differences. Even though the raw materials used to make engine oils are crude oil, the way they are processed is not quite the same. The two main things that go into making oil are

  1. Base oils.
  2. Additives.
engine oil

It’s the combination of these things that make the oil different from one another. Let’s take a detailed look at each of these types of oil that you may be confused about. Then, together, you and I will explore the differences between them in real-life use cases.

What Is Regular Or Conventional Oil?

Conventional engine oils have been in use for the longest time. It is the type of oil that usually comes at the cheapest price. That’s because it goes through the least amount of refining.

conventional motor oil

At first, crude oil is collected that sits underground for long periods of time under high pressure. This oil is extracted, boiled, and refined to be converted into mineral oil.

Then, the oil goes through certain formulations depending on the brand that’s making the oil. At this stage, additives are also added and the oil is bottled to form the final product. 

What Is Synthetic Oil?

When oils are extracted and refined, the molecules in them have a strong but randomized structure. That’s what you get when you opt for a conventional oil. The problem is that engines won’t perform at a top level when the hydrocarbons in them have so much randomness.

synthetic motor oil

That is what essentially creates the need for synthetic oil. When it comes to synthetic oil, they undergo a lot more refinement. Through decades of research, several oil manufacturers and engineers have figured out methods to make the molecular structure of the oil more uniform.

So, the molecular structure of the oil becomes less random. The refinement of the oil also removes many impurities present in the oils. The end result is that it’s smoother for the engine.

Because synthetic oils need to undergo more refinement, they are more expensive than conventional oils. But you’ll get enhanced performance if you use them and they also tend to last longer. So, you’ll have to decide if it’s worth it for you to switch to a synthetic oil if you’ve been using a conventional oil.

What Is The Difference Between Regular And Synthetic Oil?

The main point of difference between regular and synthetic oil is the amount of refinement they go through. Due to the addition of artificial chemical compounds, the petroleum molecules are rebuilt in synthetic oils.

If you were to look at a conventional oil under a microscope, you’d see millions of molecules that are of different shapes and sizes. But if you look at synthetic oils, the molecules will all have a similar shape and size.

The change in molecular structure causes a lot of differences in the performance of both these oils. The engine has a lot easier time dealing with oil that has a more uniform structure. Now, let’s take a detailed look at the main differences between a regular and a synthetic oil.

i) Engine Wear Protection

The main objective behind using synthetic oil is to protect the engine from wearing out. When a car runs, the different parts in an engine rub against one another. It’s the job of the oil to act as a lubricant and reduce the friction in different metal components.

engine wear protection

The engine oil is often the only protection that the engine has in a lot of situations. While conventional oils will offer okay protection as they will act as a lubricant. However, they can break down easily due to heat and the rubbing of engine components as they don’t have a uniform molecular structure.

When it comes to synthetic oils, they can last longer as they won’t break down as easily. They will hold their structure and act as a better lubricant for the engine. So, the engine will wear out after the longest possible time and get the maximum protection when synthetic oil is used.

ii) Protection In High Temperatures

When you drive your car, one obvious outcome of it is that the engine will get hot. Unfortunately, not all types of oil can handle that kind of heat. When it comes to conventional oil, they can easily break down in that situation.

The molecules in conventional oil don’t have the capability to tolerate extreme temperatures. So, they turn into vapor when they’re pushed beyond a certain limit. When the oil breaks down, it’ll no longer protect the engine components when they rub against one another.

On the other hand, the molecular structure of a synthetic oil is a lot more stable. So, it has the capability to withstand a lot more temperature fluctuations. It does a much better job when compared to conventional oils.

Even though synthetic oils also have their limits, they are usually capable of withstanding much higher temperatures than conventional ones. If you’re someone who drives for long durations, synthetic oil would be of great use to you as it won’t break down so easily.

iii) Cleanliness Of Engine

Conventional oil contains a lot of impurities. It often breaks down when the engine reaches a high temperature. As the oil flows through the engine, those impurities get deposited on the engine. This can easily lead to the formation of sludge in the engine.

clean engine

The end result is that the efficiency of the engine will be reduced in the short run. In the long run, the longevity of the engine will be compromised and it’ll go bad a lot faster than what it’s supposed to.

The good thing about synthetic oil is that most of the impurities from it have already been removed when the oil is made. During the refinement process, several cleaning elements are also added to the synthetic oil along with making its shape more uniform.

Not only do synthetic oils take longer to break down, they don’t produce as many deposits when that happens. So, the engine stays clean and its efficiency or lifespan is not compromised. In fact, some top-quality synthetic oils also remove sludge from the engine if it has already been built up.

iv) Flow In Low Temperatures

When you don’t use your car for a while, the oil in the car settles. But when you start a car, the oil starts to flow to the different engine components. The problem with regular oil is that it can take a long time for the oil to get activated and flow through the engine.

driving car In cold temperature

This time is greatly reduced in synthetic oil. So, if you’re using that, the oil will flow much more smoothly to the engine components in a shorter time span. Due to the molecular integrity of the synthetic oil, it can stay stable at both temperature extremes – hot and cold.

This difference in oil activation time when starting an engine is even more noticeable if you live in a colder climate. That’s because conventional oils can get thick when the outside weather is cold. They contain a layer of wax that makes them thicken up during extremely cold weather.

However, synthetic oils don’t have such a wax coating and they remain relatively more fluid even in harsh cold temperatures. So, synthetic oil should be the way to go for anyone who lives in an area where the temperature often gets freezing cold.

v) Turbocharger Protection

Since the advent of motor vehicles, the engines have kept on getting smaller and smaller. The great news with regards to that is that the performance of the engine has not gone down with its size. As a matter of fact, the fuel efficiency has been improved by a great deal in the modern engines.

car turbocharger

However, the turbocharger plays a key role in boosting the power. Any car that is equipped with a turbocharger is subject to extreme heat. They also spin really fast at the same time.

For example, it’s not uncommon for the temperature of the oil to reach or go beyond 400 degrees Fahrenheit while the shaft spins more than 200 revolutions in a minute.

It’s safe to say that a conventional motor oil can’t handle that. It’ll easily break down when it reaches such a temperature and that will reduce the efficiency and lifespan of the turbocharger.

Synthetic oils will perform a lot better as they are more reliable during extreme temperatures. The molecular stability of them will make sure that they hold up against the high speeds and the temperature of the turbocharger.

When it comes to the turbocharger, that’s not all. Using conventional oil can often lead to a phenomenon called turbo cooking. As the oil gets too hot inside the turbo, it continues to melt even when the engine is shut off. So, that can lead to deposits in the turbo.

Again, synthetic oils are much more resistant to such conditions and they’ll easily outperform conventional oils. They’ll make sure that the engine and turbo get the protection they need. If you have a turbocharger-powered car, using synthetic oil should be a no-brainer for you.

vi) Fuel Economy

When the oil in an engine doesn’t do its job properly, sometimes the engine is forced to work harder. Let’s look at it with an example. When the oil won’t flow through the engine when you start the car in cold weather, the engine will have to work much harder to get started.

It means more fuel will be required to start the car in this scenario. That’s exactly what will happen if you use a conventional oil. But if you use synthetic oil, the car will have a much easier time starting. So, it won’t take as much effort for the engine and you’ll end up saving on fuel.

vii) Oil Consumption

The engine in a car often gets hot oftentimes. As the regular oil breaks down easily when the engine gets hot, they don’t last for a long time. So, you’ll run out of oil and you’ll soon need a refill if you use this oil.

On the contrary, synthetic oils remain more stable even in high temperatures. As they don’t break down so easily, you can expect them to last for much longer periods. 

What Is The Difference Between Full Synthetic And 100% Synthetic Oil?

A lot of people use the terms 100% synthetic oil and full synthetic oil interchangeably while others don’t. In fact, there’s a group of people who don’t even consider full synthetic oil to be real synthetic oil. What’s up with that?

difference between several synthetic oils

Let’s start by breaking down what these terms mean. An oil is said to be 100% synthetic when it’s made with Group IV or Group V base oils. On the other hand, oils that are made from Group III oils are called full synthetic oils.

So, why are these base oils such a big deal? That’s because the characteristics of the oil change significantly between the different base oil groups. That’s why API has put them into different categories.

Group I and II are known as conventional base oils. The reason that many people don’t consider full synthetic oils to be synthetic is that they are made from Group III base oils. Historically, there has been debate about whether this base oil qualifies as synthetic or not.

However, this question was answered in a lawsuit in the late 1990s. Mobil brought Castrol to court as they were making oils from Group III base oils and marketing them as synthetic oil. The court ruled in favor of Castrol and thus it became real. Group III base oils are also synthetic oils.

Along with Group III oils, Group IV and V base oils are also synthetic oils. The higher the group of the base oil, the higher the quality it is. For example, Group IV base oil is superior to Group III base oil.

As for the terms full synthetic and 100% synthetic oil, they’re only used for marketing purposes these days. A brand can use any of these terms to refer to its line of synthetic oils.

The only requirement is that the base oils must be from Group III, IV, or V. If there’s any trace of Group I or II oils, it will have to be marketed as a synthetic blend. They can’t market it as synthetic oil.

So, that leaves a lot of gray areas even within the synthetic oil. Even if an oil company uses 99% Group III base oil and 1% Group IV oil, they can market their oil as synthetic. That’s why you have to be careful when picking a synthetic oil to make sure that you’re getting a good deal.

Finally, always consider that additives are an equally important part of determining the quality of oil. No matter how good the base oil is, it’ll be useless if the quality of additives is not good.

For these reasons, it is important to pick the oil of the right brand. If you’re struggling to pick the right oil for you, I got you covered. Check out my guide on the top-performing high-zinc oil brands to find out about some potential options for you.

Does Synthetic Oil Have Any Disadvantage?

Given the numerous benefits that one can enjoy using synthetic oil, you may wonder why everyone just wouldn’t use synthetic oil. Based on my personal experience, there are two main reasons behind that. Let’s take a look at them.

i) Cost

The hefty price of synthetic oil is probably the biggest reason why people don’t use it. To be honest, it makes sense as it may not be the right choice for all people. There’s no need to spend the extra bucks if your car doesn’t need it.

Synthetic oils generally cost two to three times more compared to conventional oil. However, they also do last longer than regular oil. So, people often overestimate how much they’re actually spending more to use synthetic oil.

I’ll break down the math of how much extra a person really pays when using synthetic oil. Keep on reading to find out that. But keep in mind that if your car requires synthetic oil, don’t cheap out on the oil as it’ll lead to major problems in the long run.

ii) Past Reputation

Another big reason behind not using synthetic oil is the reputation it has on older cars. When synthetic oils first came into the scene and were used, they damaged a lot of cars. It’s completely true and nobody should deny that.

Due to the damage it did in the past, a lot of people are still reluctant to use synthetic oil even today. But the fact of the matter is synthetic oils have been greatly improved since they were first introduced.

Oil manufacturers have spent a lot of their money and resources to come up with better formulations for synthetic oils. Even though they did cause damage in the past, you can’t compare the newer synthetic oils with the past.

If your car doesn’t need synthetic oil, then it’s still understandable to not use it. But if your car manufacturer clearly states that you need to use synthetic oils, don’t let your past experiences hold you back. These modern synthetic oils are a lot more improved than what they used to be.

Is Synthetic Oil Worth The Extra Cost?

Whether it’s wise to spend additional money to use synthetic oil is a question that still confuses many people. The truth is it’s not that easy to answer this equation as there’s a lot of gray area when it comes to the difference between synthetic and conventional oil.

First of all, there’s the consideration of what type of synthetic oil is in question here. Is it 100% synthetic oil or another type? What about the quality of additives used and the oil brand?

These questions can easily alter the answer. However, let’s look at it from a general perspective. An average oil change with conventional oil costs about $40 on average whereas that with synthetic oil costs about $75.

The frequency to change a conventional oil is generally every 3000 miles for a conventional oil. When it comes to synthetic oil, the average oil change interval can be 5000 miles. Now, let’s say you are a person who drives 12,000 miles on average per year.

So, using conventional oil will require 4 oil changes in total for you and cost $160 per year. But if you use synthetic oil, you’ll need 2 oil changes and a little more than that. I did the math and it adds up to spending $180 on average. So, you’re only spending $20 more if you’re using a synthetic oil.

Again, this was a very general example. It can all differ based on the brand, viscosity, and other factors that your car needs. But you can do a maths like this yourself to figure it out for you. If you only need to spend a little extra to use synthetic oil, I think it’s well worth it.

Keep in mind that using synthetic oil should only be a choice if using synthetic oil isn’t necessary for your car. If your car manufacturer recommends it, you should use synthetic oil even if you have to pay extra for it. But ultimately, it’ll be your choice and you’ll have to take the final call.

When Is Synthetic Oil The Right Choice?

If your car manufacturer doesn’t explicitly tell you to use a synthetic oil, you can get away without using it. Even though a case can be made that you can use synthetic oil in them too, let’s forget about them for now.

There are some scenarios in which you should use synthetic oil without any doubt. I’ve made a list of them. If any of them apply to you, using synthetic oil will surely be the right choice for you.

i) Heavy Duty Performance

If you’re one of those people who like to push your car to the edge, you should use synthetic oil. If you have a high-end sports car and you love to drive it fast, your engine will get heated.

car heavy duty performance

I’ve already talked about how synthetic oil is so much better than conventional oil in engine protection considering such conditions. Use synthetic oil to get a more efficient engine performance from your car.

ii) Extreme Weather Conditions

Synthetic oils are better suited to perform in both extreme hot and cold weather. Regardless of the weather, you’ll be much better off using a synthetic oil rather than a conventional one.

That’s because synthetic oil won’t break down as easily as its conventional counterpart in hot weather. On the other hand, it’ll flow much more easily in cold weather compared to regular oil.

In both scenarios, synthetic oil wins the battle and is the better choice by far. If you want to avoid issues related to cranking and oil pressure, stick to synthetic oil and you’ll be fine.

iii) Luxury Vehicles

This is a fairly obvious one. If you afford a top-of-the-line vehicle for yourself, there’s no doubt that you shouldn’t be cheap on the oil. Luxury vehicles even require synthetic oil and it’s recommended by the manufacturer.

luxury car

Even putting all that aside, it’s just common sense that you should use the best oil available to you. Only that can ensure superior performance and reliability from it. 

iv) Longer Drain Periods

I have never met anybody who likes frequent oil changes. If you want to delay oil changes as much as possible without harming your car, using synthetic oil is the right choice for you.

oil draining

Synthetic oil generally has a much longer change interval than conventional oil. Sometimes, it can even be twice the conventional oil. That means you’ll have to change the oil half the times compared to the regular oil. 

v) Harsh Driving Conditions

There are a lot of factors that can lead to harsh driving conditions. I already talked about the weather. But even apart from that, the terrain and the number of hours spent each day driving are also important points to consider.

If the driving conditions are extreme, that’s when there are maximum chances of the oil thinning out. To prevent the engine from wearing out due to it, using synthetic oil will be the right choice in these cases.

vi) Long Engine Life

I saved the best for last. This is perhaps the biggest factor that you should take into account when deciding which type of oil you want to use. If you’re someone who doesn’t intend to use a car for a long period, it may not be worth it to invest in a synthetic oil.

But if you want to use it for the foreseeable future, synthetic oil can be the right choice for you. In other words, you should use synthetic oil if you want to get every possible mile out of your car.

The majority of the difference will be made in the mind when the car has been around for a long time. For example, a car that has been driven for 200,000 miles will have a significant difference between them based on which oil was used. It’s up to you what you want to choose.

With those common scenarios out of the way, it’s important to mention that sometimes the answer won’t be as clear. In that case, you’ll have to exercise good judgment to choose the right oil type for you.

What Is Semi Synthetic Oil?

When you think of a completely rudimentary oil for a car engine, that’s the regular or conventional oil. On the other hand, the most advanced and engineered oil for supreme performance for the car engine is synthetic oil. Semi-synthetic oil is the bridge between the two.

As the name suggests, semi-synthetic oil isn’t fully synthetic oil. So, what does that mean? In simple terms, semi-synthetic oils are made when conventional oil is mixed with synthetic oils. So, they’re not fully synthetic, and at the same time, they’re also not fully conventional.

The funny thing about synthetic blends is that there is no fixed ratio of regular and synthetic oils in them. So, there’s a lot of grey area that oil manufacturers can play with to call an oil a synthetic blend.

For example, an oil that has 99% conventional oil and 1% synthetic oil can be named a synthetic blend. The reverse of that is also true. So, adding any amount of synthetic oil to a regular oil qualifies it to be a semi-synthetic oil.

As oil makers don’t have to reveal the composition of each oil in a synthetic blend, they may try to take advantage of this by putting very little synthetic oil in it. Luckily, there are some guidelines you can follow as a consumer to make sure that you’re getting good-quality synthetic oil.

Firstly, look at the VI or viscosity index of the oil. If it’s on the higher end, I’ll bet that the synthetic blend contains a much higher ratio of synthetic oil than the lower VI ones.

Secondly, the pour point of an oil is also a good indicator of the composition of oils in a synthetic blend. Generally, the lower the pour point in an oil, the more synthetic oil will be in that blend.

Hopefully, you can use the above pointers to find out the right synthetic blend for your car. If your car only requires a conventional oil, you’ll be fine using a synthetic blend. But if it needs a fully synthetic oil, then make sure that you use that instead of a cheaper one.

What Is The Difference Between Semi Synthetic And Regular Oil?

Conventional oil is made from crude oil. But you get a synthetic blend when that conventional oil is mixed with synthetic oil. So, it performs better than conventional oil but not as good as full synthetic oil.

Using a semi-synthetic oil is a more economical option than using synthetic oil  for those who only require a conventional oil. It’s ideal for those cars that only require conventional oil but the owner wants a little more protection without necessarily getting a full synthetic oil.

What Is The Difference Between Semi Synthetic And Synthetic Oil?

Synthetic oils don’t have any regular oil in them. They have been refined to the point where they have a stable and uniform molecular structure. However, synthetic blends or semi-synthetic oils have both synthetic oils and regular oils in them.

Simply put, semi-synthetic oil is better than conventional oil but not as good as synthetic oil. But synthetic blends are also priced lower than synthetic. However, if your car manufacturer requires you to use a synthetic oil, using a synthetic blend won’t cut it.

Are Synthetic Oils Good For The Environment?

A lot of people think that synthetic oil is environment-friendly due to its name. Their logic is if it applies to leather, it must also apply to oils. Unfortunately, that’s not how it works.

If you’ve been paying attention to this guide, you’ll realize that both conventional oils and synthetics have the same raw material. They’re both made from crude oil. And that’s a fossil fuel.

As the raw material is a fossil fuel, whatever you make from it won’t be friendly to the environment. At the very source, it’s not good for the environment. So, if you think that synthetic oils are good at protecting the environment, that hypothesis is completely wrong.

That is not to take away the fact that synthetics will always perform better than conventional oils. But if going environment-friendly is your number one priority, then you should switch to an E-vehicle. There is no point in lying to yourself about the products you’re using.

How Are Motor Oils Rated?

Engine oils have been around for a long time. Being in use for so many years, it’s evident that there is a need for standardized testing systems to rate the quality of oils. This rating system is developed by the Society of Automotive Engineers or SAE.

You should look at the oil bottle whenever you get one and make sure it meets these standards. In both the front and back of the bottle, you’ll see these ratings in qualified oils. Let’s look at the most common rating metrics for oil.

i) API/ILSAC Starburst

ILSAC stands for International Lubricant Standardization and Approval Committee. It’s a joint venture by American and Japanese automobile companies to rate the quality of oil.

You should see this sign in the front of the vehicle. This starburst is useful as it tells the specific use case of that oil. For example, you may come across the words “For gasoline engines” if you look at it. Here’s an example of how this starburst sign looks:

ap or ilsac starburst

If you looked carefully, you must have seen that the outer label of the seal says API certified. API stands for the American Petroleum Institute. This seal is given to an oil when it meets the minimum industry standard requirements. 

ii) API Donut

If you look at the back of the oil bottle, you’ll find the API rating of the oil. It’s different from the API Starburst seal. The starburst is only a signal that the oil passes the minimum standards. However, the API rating reveals a lot more information about the oil. Here’s what it looks like:

api donut

The top part of the label shows the API rating of the oil. An oil could fall under several ratings based on its performance and the elements inside it. SM and SJ are some examples of API ratings. I’ll explain the different API ratings given to oils in the next section in detail.

The center of the API label represents the viscosity grade of the oil. It explains how thick or thin the oil is. If the number is low, the oil is thin and if the number is high, the oil is thick. I’ll also discuss this topic in detail in a later section of this guide.

Finally, there’s the bottom part of the label. It reveals if the oil has shown any properties related to energy saving. If it does, that is mentioned at the bottom of the label. If not, the API rating is often repeated at the bottom. 

How Are Oils Given API Ratings?

Let’s look into API ratings in more detail starting with it’s format. If the rating is of two letters and starts with S, the oils are designed for gasoline engines. The S stands for Service Station oils and the next letter is the actual rating of the oil. For example, SM and SN API ratings.

You may also come across API ratings that begin with a C. If the ratings start with a C and have the number 2 or 4 at the end, they’re made for diesel engines. The C stands for Commercial engines.

The next letter after C denotes the current rating of the oil. The number 2 or 4 at the end represents whether the oil is made for a 2-stroke or a 4-stroke engine. For example, CJ-4 and CI-4 are API ratings of oils for diesel engines.

But why is there a need for API ratings in the first place? As car engines have improved, the need for improving engine oils has also increased. So, API ratings are a great way to identify the improvements in oils.

The automotive parts get more advanced with time. To be compatible with these parts, engine oils need to be updated in terms of their viscosity, protection capability, etc. When newer oils are developed to match these requirements, they’re given new API ratings.

You need to know that API ratings are backward integrated. So, the oils that have the latest API ratings can be used in cars that require a lower API rating. It’s safe to choose the latest API-rating oil in most cases, especially, if your car is no more than 10 years old.

So, how do API ratings work? I’ll go through the API rating of both gasoline and diesel engines so that you have the perfect idea of it. Let’s start with the API ratings for gasoline engines. Here it is:

  • SJ API Rating: This oil is suitable for vehicles that were manufactured between 2001 and 2004.
  • SM API Rating: This oil is suitable for vehicles that were manufactured between 2004 and 2009.
  • SJ API Rating: This is the latest API rating for oils and this is the right rating for vehicles that were made after 2010.

Similarly, there is a rating system for diesel engines depending on when they were made. It looks like this:

  • CH-4 API Rating: This oil is suitable for vehicles that were manufactured between 1998 and 2002.
  • CI-4 API Rating: This oil is suitable for vehicles that were manufactured between 2002 and 2010.
  • CJ-4 API Rating: This is the latest API rating for oils and this is the right rating for vehicles that were made after 2010.

This was just a rundown of the most recent API ratings. Oils used to be rated from a much earlier period. For example, oils that were made in vehicles manufactured in the 1920s have an SA API rating.

I’ve only talked about the API ratings of vehicles that’ll be useful for you. The performance of the oil is judged on its ability to protect against wear, the build-up of deposits, efficiency at low temperatures, etc. For gasoline engines, you’ll find oils rated between SG and SN these days.

Remember that it’s all good to stick with the latest API rating as that’s the most advanced oil you can use at that time. It gives your engine the maximum chance of performing well and staying in optimal condition in the long run.

What Is Single Grade And Multi Grade Oil?

You may have often come across the word “viscosity” when looking for oils. In simple words, it determines the thickness of the oil. The lower the viscosity of the oil, the thin it is. The higher the viscosity, the more thick the oil is. Oils are also rated on viscosity and this system was also developed by SAE.

If the oil has low viscosity, it flows like water. If it has a high viscosity, it flows like honey. So, the viscosity of an oil also determines the resistance that it’ll flow at. The thing about engine oils is that they’re exposed to different temperatures and their viscosity may change according to them.

When oils were first introduced, they only had one viscosity. Those are single-grade oils. But as they continued to be developed, oils that could have variable viscosities were introduced in the 1950s. Those types of oils are called multi–grade oils.

The development of multi-grade oils was extremely important in dealing with the fluctuations in temperatures and engine operating conditions. If you live single-grade viscosity oils, it will only have one number. For example, it could be SAE 30.

However, multi-grade viscosity oils will have two numbers. For instance, they could be SAE 5W30. Now, the W here stands for winter and the number before that represents the viscosity of oil at cold temperatures. The number after the W is for the viscosity of engine operating conditions.

When you start the car, the engine is cold. So, it’ll flow at the number before the W. But when it reaches the operating conditions, it’ll flow at the number after W. So, multi-grade oils are great to make sure that the oil has good flow in low temperatures and good protection in high temperatures.

If you have a 0W30 and a 10W30 oil, the 0W30 oil will flow better at low temperatures. But they’ll both offer the same protection in high temperatures. So, the 0W30 oil is better in this case. However, keep in mind that this is with the assumption that all other things between the two oils are the same.

The performance of the oils can always change based on the formulation and the additives. Always follow the recommendation of your car manufacturer when picking an oil. It’s okay to upgrade but not to downgrade. Hopefully, you no longer have any confusion about oil viscosity now.

How Important Are Additives In The Performance Of Oil?

When it comes to choosing the right oil, people are often focused on just the rating and viscosity of the oil. But if you have noticed properly, you’ll see that oils with the same specs have different performances depending on the brand. Have you ever considered why that happens?

The simple answer behind that is additives. Even though oils of different brands can have the same base stocks, the additives make all the difference. That’s why oils of the same brands outperform others depending on the vehicle on which it’s being tested.

Oils won’t be able to fulfill their duty nearly as well as they do without additives. Oil additives are essentially chemical compounds that are added to oil for several reasons.

What Are The Different Types Of Oil Additives?

You’ll have a much better understanding of why additives are important and the role that they play if you learn about the different types of them. So, let’s look at the most common oil additives.

i) Viscosity Index Improvers

As you know, the viscosity of the oil changes depending on whether the engine is cool or hot. It’s the role of VIIs to make sure that the fluctuations of the oil viscosity stay within an acceptable range.

ii) Antioxidants

The oxygen in the air reacts with the engine components and makes them wear out sooner. Even though it happens in all temperatures, the worst of it takes place when the engine is too hot. Especially, under the presence of water.

The end result is that acid is produced and it leads to the formation of sludge in the engine. Along with that, the engine components also start to get corroded with the passage of time.

However, all of that is significantly slowed down due to the presence of antioxidants in oils. They are self-sacrificial compounds that themselves get damaged in order to protect the base oil and the engine. They’re so important that they’re present in all lubricating motor oils.

iii) Corrosion And Rust Inhibitors

The engines are protected from internal rust through the use of these inhibitors. They neutralize the acid and form a protective barrier to prevent the formation of moisture on the metal surfaces.

They are typically made with barium sulfonate and calcium. Some of them are designed to protect specific types of metals. So, it’s not uncommon to find many types of corrosion and rust inhibitors in a single oil.

iv) Antiwear Agents

ZDDP or Zinc dialkyl dithiophosphate is the most common type of antiwear agent used in oil. It’s essentially a mixture of Zinc and Phosphorus that makes sure the engine doesn’t wear out due to the rubbing of metal surfaces.

The additives do that by attaching themselves to the metal surfaces and forming a surface. Not only does it increase the lubrication but also minimizes the wear of engine components.

v) Detergents

Detergents and dispersants together play a significant role in making sure the oil performs well. The detergents in oil make sure that the metal components are free of deposits as they get burned. It also plays a key role in neutralizing acids. They’re crucial to prevent the build-up of sludge.

The most common types of detergents that are put in oils these days are combinations of Calcium and Magnesium. Barium-based detergents were used a lot in the past but they’re not used that much these days.

vi) Dispersants

Think of dispersants as partners to detergents in keeping the engine clean. As the detergents remove the impurities, they’re suspended by the dispersants. This is done to prevent the impurities from settling on the metal components.

If it wasn’t for the dispersants, the solid particles would react with the metal parts, and the detergents wouldn’t be effective. But as they remain suspended, they can be easily removed during an oil change.

vii) Antifoaming Agents

The presence of antifoaming agents in oil makes sure that the foaming of oil is reduced as it moves through an engine. Without it, there would be a lot of surface tension between the engine oil and the air bubbles. It can lead to more oxidation and rusting of the internal components.

However, it is prevented with antifoaming agents by making the bubbles easy to pop. Usually, this additive is required in very low quantities like less than 20 parts per million. If it’s used excessively, it’ll have a reverse effect and make the performance of the oil much worse.

viii) Friction Modifiers

Good-quality oil improves the fuel economy of an engine with the help of friction modifiers. They’re used to reduce the friction between the different parts of an engine.

Along with engine oil, they’re also used in transmission fluids for the same purpose. It makes the performance of the clutch materials a lot better.

ix) Pour Point Depressants

This is an extremely important additive when it comes to multigrade oils. It determines the lowest temperature at which the oil will stay fluid. There are wax crystals that solidify at low temperatures and that makes the oil thick.

It also prevents the oil from flowing properly. The pour point depressants reduce the size of these crystals by reacting with them. That enables the oil to flow at much lower temperatures.

Should You Use Aftermarket Additives?

Additives are put into the oil by the oil manufacturers themselves. Besides them, there are also aftermarket or supplemental oil additives that are available for use. So, are they worth using?

In simple words, my answer will be no. That’s because the use of these additives won’t magically turn a bad engine oil into a good one. It’s much better to invest in a good engine oil that won’t need these additives in the first place.

Besides, certain engine oils may not be compatible without some aftermarket additives. In that case, they could be useless or even harm your engine. Oils can only handle a certain amount of additives. If they’re already there, then adding more additives will make it extremely saturated.

A lot of the companies who make these additives also tend to overpromise on the benefits that one can expect after using them. So, be sure to ignore the clever marketing they use.

With that said some aftermarket additives have indeed shown improved performance in engines. If you are an expert and you understand what type of additives your oil needs, you can try out additives.

Make sure you choose an additive that has been proven effective in independent field testing. If you don’t have any expertise on it, then you’re better off ignoring it altogether.

How To Know Which Type Of Oil To Use For Your Car?

When it comes to choosing the right oil, a lot of people are worried about whether to choose synthetic or conventional oil. Frankly, that’s not the only thing you should consider as you’re aware of API ratings and oil viscosity.

All these factors are equally important. Picking the right oil for your car is easy. If you look at your owner’s manual, you’ll find the exact oil type you need. It’ll not only say whether you require synthetic or conventional oil, but you’ll also learn about the required viscosity and API rating.

Just follow that recommendation and you’ll be fine. But you should also remember that upgrading of oil is okay but downgrading is not. For example, if your car manufacturer says that you need a conventional oil, you can still use a synthetic oil if you want.

But if your car requires a synthetic oil, you can’t use a synthetic oil. Similarly, if your car manufacturer recommends a 5W30 oil, you can use it. You’ll also be fine if you use a 0W30 oil as it’ll have better flow at low temperatures. But you shouldn’t use 10W30 oil as it’ll have a worse flow when you start the engine. 


Is it normal to mix synthetic oil with conventional oil?

Mixing synthetic and conventional oils is not harmful to your car’s engine in any way. If you think about it, synthetic blends or semi-synthetic oils are essentially just that.

What is advanced full synthetic oil?

It’s just a marketing term and that’s what Mobil calls their line of synthetic oils. They’re also synthetic oils that are made from either Group III, IV, or V base oil along with some additives.

When is conventional oil the right choice for a user?

Even though synthetic oil is always better than conventional oil, synthetic oils aren’t always required. For cars that have simple engines and are driven in regular conditions rather than severe ones, conventional oil is a good choice.

Is it safe to use expired oil in the engine?

When engine oil expires, it won’t offer the lubrication and protection that the engine requires. So, the engine will be damaged due to it in the long run. You should always use oil that is fresh to prevent these problems.

Are older API-rating oils compatible with newer engines?

While oils that have the latest API ratings are fit for use in older cars, the reverse of that is not true. Oils with old API ratings are not fit for use in modern cars. If they were, there would be no need to develop new oils.


By now, you should easily know the differences between the major groups after completing this regular vs synthetic vs semi-synthetic oil guide. As you move from regular all the way through synthetic, the oils get more refined. Unlike food, the more refined an oil, the better it is.

That’s why if you just want to get the highest-performing oil without worrying about the price, you can get synthetic oil. Otherwise, you can consider the other options. Amsoil has a great line of synthetic oils. I have a guide on Amsoil synthetic oils that you may want to check out.

About John M

John contributed as a technical head at an automobile company just 2 years after his post-graduation in Automobile Engineering. He loves to lead a free life, so he left his job & started blogging. Now, he does research on every automotive problem, part & product and seeks a better solution & best products & shares his findings with his readers to help them as well as to minimize their struggle.

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