The difference between 10w30 vs. 10w40

Automobiles need oil in their engines for lubrication purposes. Since a gasoline engine is comprised of hundreds of moving parts and actions, they generate a lot of heat. If there is no lubrication for the moving parts, they will create friction and wear out fast. That is why oil is so essential.

Not all oil is the same, though. There are different viscosity grades for oil, which basically refers to their level of thickness and weight. Two standard viscosity grades you’ll see are 10W30 and 10W40. These are considered multi-grade oils because they have a grade before the “W” and after the “W.”

In the old days, there was only one grade for summer and winter. That means you had to switch your oil each season. Now, we have multi-grade oils that are good for both summer and winter use. But the specific multi-grade oil you choose depends on the climate of your environment and the vehicle itself.

Contrary to popular belief, the “W” doesn’t mean “Weight.” It means “Winter” because your environment’s temperature plays a critical factor in which oil you choose.

The number before the “W” is the viscosity, which signifies the level of thickness and stickiness of the oil as it gets colder outside. The number after the “W” indicates the oil’s flow quality within the engine as the temperature is hot. Heat is generated by both the outside temperature and the engine.

It would help if you took it upon yourself to learn the difference between the two grades. Not only could it prolong the life of your gasoline engine, but it will improve the horsepower and fuel economy as well.

Let’s discuss the difference between 10W30 and 10W40.


10W30 and 10W40 both have one thing in common: the “10” before the “W.” 10W viscosity is thicker oil when cold, so it is suitable for hotter environments. When the number before the “W” is high, it always means the oil is thicker and ideal for hot climates.

But if the number were 5W or 0W, it means the oil is thinner and better for colder environments. The “30” following the “W” means it flows better when the engine temperature is hot. More importantly, it signals that it will lower the temperature of the engine and keep it cooler.

When the 10 and 30 are combined, it creates a multi-grade oil that can last both seasons. However, it doesn’t mean 10W30 is the best for both seasons. Auto mechanics will tell you that 10W30 is better for hotter engines in colder environments. But if you were living in a warmer environment, they’d probably recommend 5W30 because it is thinner when cold.


When exposed to hotter engine temperatures, 10W40 is better than 10W30 inside of an engine as it flows. 10W40 is also recommended for colder outside environments because it has the 10W in front of it too. Anytime you see the 10W, then it is good for a colder environment. But because the 40 is higher than the 30 after the W, it means the oil can handle hotter engines.

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People consider 10W40 to be an oil that prevents overheating issues. The oil is highly sticky within the engine, so it sticks to various moving components and lubricates them continuously.  10W40 is not much different than 10W30 other than it adds more protection to your engine.

Just make sure your car doesn’t sit outside for too long with 10W40 oil in it. Otherwise, it might thicken too much and give you trouble starting the vehicle. Try to keep your car parked inside your garage where proper heating exists. If you live in the south already, then don’t worry about it.

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