Which oil is right for your car: 5W30, 10W40, 15W40, or 20W50?

Choosing engine oil isn't simply a matter of "any kind will do." For many car owners, symbols like 5W30, 10W40, 15W40, or 20W50 are often confusing, yet they directly affect lubrication, engine smoothness, fuel efficiency, and engine lifespan.

In reality, there is no single type of oil that is suitable for all types of vehicles. Each viscosity grade is suited to different operating conditions, engine conditions, and usage environments.

So, what are the differences between 5W30, 10W40, 15W40, and 20W50 oil? Which type is suitable for new cars, used cars, or commercial vehicles? Let's find out more with Gartz.

What are 5W30, 10W40, 15W40, and 20W50 engine oils?

These are the viscosity grades of engine oil according to SAE standards. Each symbol indicates the thinness or thickness of the oil under different temperature conditions.

For example:

5W30
10W40
15W40
20W50

The number before the "W" indicates the engine's low-temperature operating capability. The smaller the number, the thinner the oil becomes when the engine is cold, allowing for faster oil pumping during startup.

The number after the number indicates the viscosity when the engine reaches operating temperature. The higher the number, the thicker the oil becomes when hot.

The meaning of the symbols on engine oil

Many people think that the thicker the oil, the better, but the reality is not that simple.

For example:

5W30: Thins out when hot, helping to save fuel and run the engine smoothly.
10W40: A balance between protection and flexibility
15W40: commonly used for light trucks, high-mileage vehicles, or older engines.
20W50: thicker oil, suitable for engines with large clearances or older vehicles.

It is important to choose the right option based on the manufacturer's recommendations and the actual condition of the vehicle.

Which vehicles are suitable for 5W30 oil?

5W30 is commonly used for:

New car
Modern Japanese and Korean cars
Many cars are driving in the city.
Fuel-efficient vehicles
The engine features fuel injection, turbocharging, or hybrid technology.

The advantage of 5W30 is that the oil heats up quickly when the engine is cold, reducing friction during startup and supporting smoother engine operation.

However, with very old vehicles or heavily worn engines, oil that is too thin can sometimes cause the engine to overheat or consume more oil.

Which vehicles are suitable for 10W40 oil?

10W40 is a fairly common viscosity grade because it's easy to use for many different types of vehicles.

This type of oil is generally suitable for:

Everyday vehicle
The car has traveled a considerable distance.
The car needs better protection when the engine is hot.
Operating conditions with higher temperatures or heavier loads.

Compared to 5W30, 10W40 generally provides a smoother engine feel and better protection at high temperatures.

This is also a popular choice for many garages for cars that have been used for many years but are not yet too old.

Which vehicles are suitable for 15W40 oil?

15W40 is commonly found in:

Xe diesel
Light trucks
The service vehicles run continuously.
The engine has a high operating temperature.
The vehicle needs oil with good stability.

A key characteristic of 15W40 is its ability to maintain a relatively good oil film under heavy load or long-distance driving.

However, for newer passenger cars that require thinner oil for optimal fuel economy, 15W40 may not be the best choice.

Which vehicles are suitable for 20W50 oil?

20W50 is a fairly thick oil, commonly used for:

Old cars
The engine is very worn.
The car consumes too much oil.
The vehicle operates in a high-temperature environment.

Some car owners prefer using 20W50 because it makes the engine feel "smoother". However, oil that is too thick can make the engine sluggish, increase the load on the oil pump, and is not suitable for many modern engines.

If your vehicle is currently using 5W30 or 0W20 as recommended by the manufacturer, switching to 20W50 just for smoother engine operation might not be a good option.

Is 5W30 or 10W40 better?

There is no such thing as an "absolutely better" type.

5W30 is suitable for newer cars that require fuel efficiency and smooth engine response.
10W40 is suitable for older vehicles or those requiring higher protection at high temperatures.

Most importantly:

Manufacturer's recommendation
Engine condition
Operating conditions
Car usage habits

15W40 vs 20W50: What are the differences?

Both are oils with fairly high viscosity, but:

15W40 is more versatile when the engine is cold.
20W50 becomes thicker when the engine heats up.

20W50 is typically for older engines or those with larger clearances, while 15W40 is more suitable for light trucks or heavily used diesel vehicles.

You shouldn't choose oil based solely on how smoothly the engine feels; you need to consider the overall performance and technical specifications of the vehicle.

Should you use thicker oil for smoother engine operation?

This is a fairly common misconception.

It's true that thicker oil can sometimes help reduce mechanical noise on some older engines. But what if you use the wrong viscosity grade?

Oil may circulate more slowly.
The machine is heavier.
Consumes more fuel
Affects lubrication ability when the engine is cold.

With newer vehicles, using oil that is too thick can also affect the variable valve timing system or the engine's ability to optimize performance.

Gartz suggests how to choose the right oil.

According to Gartz, oil selection should be based on four factors:

1. Recommendations from the car manufacturer

This has always been the first priority.

2. The actual condition of the engine

New cars and cars with high mileage will have different needs.

3. Operating conditions

City cars, service vehicles, heavy trucks, or long-haul vehicles will require different viscosity grades.

4. Oil quality

It's not enough to simply choose the right viscosity; you also need to select oil that meets the appropriate standards for your gasoline or diesel engine.

Gartz currently offers a wide range of engine oils with viscosity grades to suit various applications, from passenger cars to heavy-duty vehicles.

Conclude

5W30, 10W40, 15W40, or 20W50 all have their own suitable oil grades. Thicker oil isn't always better, and not all vehicles should use thinner oil.

The most important thing is to choose the correct viscosity grade according to the technical recommendations and the actual operating conditions of the vehicle.

Choosing the right option not only helps the engine run more smoothly, but also supports long-term machine protection and optimizes operating performance.