When choosing engine oil,
have you ever wondered:
"What's the difference between 0W-20 and 5W-30?"
"Does 5W-30 perform better just because the numbers are higher?"
"Is 0W-20 better for fuel economy?"
The numbers 0W-20 and 5W-30 represent the "viscosity characteristics" of engine oil.
Simply put,
they indicate how easily the oil flows at low temperatures
and
what viscosity it maintains when the engine is warmed up.
These two points serve as a guide.
However, a higher number does not necessarily mean better performance.
The key is to choose the viscosity appropriate for your engine.
This article will clearly explain the relationship between engine oil viscosity, friction, fuel economy, and protection performance, focusing on the differences between 0W-20 and 5W-30.
What do 0W-20 and 5W-30 represent?
0W-20 and 5W-30 are viscosity classifications for engine oil according to SAE.
SAE J300 classifies engine oils by their viscosity characteristics.
It's important to note that this indication primarily represents "viscosity classification" and does not encompass all oil qualities such as cleaning performance or anti-wear performance.
For example,
0W-20
5W-30
The first and second parts of these designations have different meanings.
Difference between "0W" and "5W"
The "W" after the first number stands for Winter.
0W and 5W indicate the oil's viscosity characteristics at low temperatures.
Generally, a smaller number means the oil has a viscosity grade that allows it to flow more easily for starting at lower temperatures.
Therefore,
0W can be considered a classification that handles starting and pumping performance at low temperatures more effectively than 5W.
Immediately after starting the engine on a cold morning, the oil temperature is low.
Oil tends to become more viscous as the temperature drops.
In other words, it "flows less easily" when cold.
This is why viscosity characteristics that allow the oil to flow easily at low temperatures are important.
Difference between "20" and "30"
The numbers 20 and 30 indicate the viscosity grade when the engine is warmed up.
Generally,
a 30-grade oil falls within a higher viscosity range at high temperatures than a 20-grade oil.
Therefore, when compared under the same conditions,
0W-20 is relatively low viscosity.
5W-30 is a higher viscosity grade than that.
However,
it's not as simple as "30 is thicker so it always protects the engine better"
or "20 is thinner so it's dangerous."
Modern engines are designed with consideration for the specific oil viscosity to be used.
Therefore, adhering to the manufacturer's specified viscosity is paramount.
A simple comparison of 0W-20 and 5W-30
To summarize broadly,
0W-20
flows easily at low temperatures and remains relatively low viscosity after warm-up.
5W-30
has a one-step higher low-temperature classification than 0W, and a higher viscosity grade than 20 after warm-up.
However, the actual performance of engine oil is not determined by viscosity alone.
Base oil.
Additives.
Anti-wear performance.
Oxidation stability.
Detergency and dispersancy performance.
Shear stability.
Performance is determined by a combination of various factors.
Therefore, judging the superiority of oil based solely on SAE viscosity is not possible.
Why do many recent cars use 0W-20?
In recent years, an increasing number of passenger cars specify low-viscosity oils like 0W-20.
One reason for this is the reduction of mechanical loss.
Inside the engine,
pistons.
crankshafts.
camshafts.
bearings.
oil pumps.
Various parts are in motion.
And energy is also required to move the oil itself.
As viscosity increases, the resistance to moving the oil can also increase depending on the conditions.
By appropriately lowering the viscosity, internal engine resistance can be reduced, contributing to improved fuel economy.
This is closely related to "friction loss," which was explained in a previous article.
Engine oil also has "resistance"
Engine oil is necessary to reduce friction.
However, interestingly, the oil itself also has resistance due to its viscosity.
For example, it's easy to understand if you imagine stirring a thin liquid versus stirring a thick, viscous liquid.
The more viscous the liquid, the greater the force required to move it.
Similarly within an engine, oil viscosity is a factor in mechanical resistance.
But that doesn't mean,
"the thinner, the better."
Because engine oil also plays the role of forming an appropriate oil film to protect components from each other.
The important role of oil is to "create an oil film"
If metals rub directly against each other, significant friction and wear will occur.
Engine oil penetrates between metal surfaces, forming an oil film.
This oil film prevents direct contact between the metals.
Therefore, engine oil has two requirements:
to minimize friction.
but also,
to ensure the necessary oil film is maintained.
Reducing resistance through lower viscosity while simultaneously maintaining the necessary lubrication performance.
This is a crucial point in modern engine oil technology.
What are the benefits of 0W-20?
When used in an engine that specifies 0W-20, it primarily offers the following characteristics:
Flows easily at low temperatures
The 0W viscosity classification addresses starting and pumping performance in cold environments.
Especially in cold weather, it's critical for oil to reach all parts of the engine after starting.
Tends to reduce viscous resistance
Even after warm-up, it maintains a relatively low viscosity grade of 20, which helps minimize viscous losses in compatible engines.
Aims for improved fuel economy
Reduced mechanical losses inside the engine allow for more efficient use of fuel energy.
This is why low-viscosity oil is used as one of the fuel economy improvement technologies.
What are the benefits of 5W-30?
5W-30 also has its uses.
After warm-up, it reaches a viscosity grade of 30, giving it a higher viscosity range than 20-grade oil.
Depending on the engine design and operating conditions, these characteristics may be necessary.
For example,
high temperatures.
high-load operation.
specific engine designs.
mileage and operating conditions.
Some cars also have 5W-30 specified or permitted by the manufacturer, taking these factors into account.
However,
it's not a blanket rule like "use 5W-30 for highway driving"
or "always use 5W-30 for older cars."
It's fundamental to check your vehicle's owner's manual or manufacturer's specifications.
What happens if I switch from 0W-20 to 5W-30?
This is a very frequently searched question.
Assuming both viscosities are allowed by the manufacturer for your car, changing the viscosity might alter the driving feel.
For example, switching to 5W-30 might result in changes to:
the perceived engine noise.
the rotational resistance.
oil pressure characteristics.
the feeling at high temperatures.
On the other hand, with 0W-20, you might notice differences in:
low-temperature operation.
rotational lightness.
fuel economy.
However, the actual sensation depends on many factors such as the car model, engine, oil product, ambient temperature, and driving conditions.
A change is not guaranteed.
Is it okay to switch from 5W-30 to 0W-20?
This is an area where you should not make a self-judgment.
Some engines are designed with 0W-20 in mind.
On the other hand, other engines are designed with different viscosities like 5W-30 in mind.
We do not recommend changing to 0W-20 in an engine where the manufacturer does not permit it,
simply for the reason of "it seems like it will improve fuel economy."
Oil viscosity relates to:
oil pressure.
oil film.
variable valve timing mechanisms.
timing chains.
turbochargers.
various hydraulic controls.
Please check your owner's manual or manufacturer's information first.
Does lower viscosity mean lower engine protection?
This is another common misconception.
It's not as simple as thinking "0W-20 is thin, so it can't protect the engine."
If the engine was designed for 0W-20 and uses oil that meets the specified standards, the necessary lubrication performance is accounted for within those conditions.
Furthermore, engine oil contains various additives beyond just viscosity,
such as anti-wear agents.
friction modifiers.
detergent-dispersants.
antioxidants.
Therefore,
high viscosity = high performance.
low viscosity = low performance.
This relationship is not true.
SAE J300 itself is a standard for classifying viscosity, not for evaluating other performance aspects.
Does increasing viscosity make the engine quieter?
When switching from 0W-20 to 5W-30, for example,
you might feel that "the engine became quieter."
This is because changes in viscosity characteristics can affect:
the oil film.
vibration.
mechanical noise.
rotational feel.
However,
quieter does not necessarily mean improved performance.
Similarly,
lighter rotation does not necessarily mean increased engine protection.
It's important to differentiate between subjective perception and the actual lubrication conditions required by the engine.
What is the relationship between viscosity and fuel economy?
When considering fuel economy, friction loss is important.
Not all of the energy combusted in the engine translates into power to move the car forward.
Internal engine friction.
pumping losses.
drivetrain losses.
Energy is lost in various ways.
The viscous resistance of oil is one such loss.
If viscosity can be appropriately reduced within a suitable range, internal resistance can be decreased, potentially leading to improved fuel economy.
However, fuel economy is not determined by viscosity alone.
Vehicle weight.
Tires.
Driving speed.
Ambient temperature.
Accelerator operation.
Engine control.
Various factors influence fuel economy.
Therefore,
we cannot say that "switching from 5W-30 to 0W-20 will definitely improve fuel economy by a certain percentage."
Should I use 5W-30 in summer and 0W-20 in winter?
Traditionally,
there's a notion of "thicker in summer"
and "thinner in winter."
However, modern multi-grade oils are designed to be used across a wide range of temperatures.
Therefore, it's not always necessary to change viscosity seasonally in typical Japanese driving conditions.
The highest priority should be the vehicle manufacturer's specifications.
Owner's manuals may specify permissible viscosities and ambient temperature conditions.
The basic rule is to choose based on that information.
Should vehicles with high mileage use a higher viscosity?
As mileage increases,
internal clearances.
seals.
oil consumption.
compression.
These conditions may differ from when the car was new.
Therefore, some vehicles may require a reconsideration of viscosity choice.
However,
a blanket judgment like "always use 5W-30 if it has run 100,000 km" cannot be made.
If there are symptoms such as high oil consumption,
increased abnormal noises,
or abnormal oil pressure,
it's important to first check the vehicle's condition rather than simply changing the viscosity.
Is 5W-30 better for turbo cars?
Turbochargers are components that operate at high temperatures and high speeds.
Therefore, oil management is extremely important.
However,
it's not always "5W-30 for turbos."
Today, some turbo engines specify 0W-20, among others.
Do not decide based solely on the presence of a turbo; confirm the viscosity and specifications designated by the manufacturer for that particular engine.
Don't choose oil by viscosity alone
For example, not all 0W-20 oils are the same.
Engine oils have various standards in addition to SAE viscosity.
Oil performance includes many aspects such as:
oxidation stability.
wear protection.
cleanliness.
sludge inhibition.
low-temperature performance.
fuel efficiency.
LSPI mitigation.
timing chain wear protection.
Even the API engine oil certification system specifies multiple performance tests, not just viscosity.
In other words,
"all 0W-20 oils are the same" is not true.
It's important to check that the oil meets the necessary standards for your car, along with its viscosity.
Relationship with engine oil additives
In the previous article, we discussed engine oil additives.
Viscosity is also important here.
Adding additives to oil later can affect the overall viscosity characteristics of the oil, depending on the product.
Therefore,
it's not always safe just because you're using manufacturer-specified oil.
And it's not okay to add anything to it.
It's important to consider the combination of:
oil.
additives.
engine.
Next Science's perspective on "viscosity and friction"
At Next Science, we consider "friction and lubrication" as one of the crucial research areas when evaluating the performance of vehicles and machinery.
Engine oil is not merely required to provide good slipperiness.
It needs to form an oil film where necessary.
Prevent wear.
Manage heat.
Carry away contaminants.
And suppress unnecessary friction loss.
It must fulfill multiple roles simultaneously.
That's why viscosity is also not a simple matter of,
"softer is better"
or "harder means more protection."
The important thing is to maintain the lubrication conditions required by the machinery while minimizing unnecessary resistance as much as possible.
Next Science researches friction and lubrication from this perspective of "balancing necessary lubrication and unnecessary resistance."
Summary: 0W-20 and 5W-30 are not about "which is superior"
The major difference between 0W-20 and 5W-30 is their viscosity characteristics.
0W-20
flows easily at low temperatures and maintains a relatively low viscosity after warm-up.
5W-30
has 5W characteristics for low temperatures and a higher viscosity grade than 20 after warm-up.
Low-viscosity oils have the advantage of being able to reduce mechanical losses.
On the other hand, it is also important for the engine to secure the necessary oil film.
Therefore,
it's not about "which of 0W-20 and 5W-30 is superior,"
but rather,
"which is more suitable for that particular engine?"
First, check the manufacturer's specified viscosity and standards.
Then, consider the operating environment and vehicle condition.
This is the basic principle for choosing engine oil.
Just as the car's performance isn't solely determined by horsepower and torque, engine oil cannot be judged merely by "larger or smaller numbers."
Friction.
Lubrication.
Viscosity.
Friction loss.
Understanding these relationships makes the role engine oil plays in car performance clearer.