Is 10w30 Thicker Than 10W40?

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Motor oil viscosity is one thing you shouldn’t joke with. Yes, there’s nothing wrong with using a thicker or thinner oil for your car’s engine, but if you need the engine to run at its best, you have to stick with the exact oil viscosity (weight) recommended by the OEM.

But how do you know a thicker or thinner oil? Is 10W30 thicker than 10W40 oil? No, 10W30 is not thicker than 10W40; instead, it is the other way round – 10W40 is thicker than 10W30. The difference between 10W30 and 10W40 is their performance at cold temperatures.

This article clearly details the difference between these two oil viscosity ratings.

Is 10w30 Thicker Than 10W40?

10W30 and 10W40 are oil viscosity ratings that indicate how the inscribed motor oil would flow at high and low temperatures, respectively. The “W” that separates the numbers stands for “winter.”

The number before the “W” indicates how the oil would flow in cold/low temperatures (usually during winter), while the number after the “W” indicates the oil’s performance at high temperatures (usually during summer).

So, with this explanation, it’s clear that 10W30 and 10W40 have the same winter flow rate of “10” but different summer flow rates of “30” and “40,” respectively. Now, what does this imply, and which oil is actually thicker?

Let’s pick the 10W30 oil. This motor oil is usually the preferred choice for most small car drivers (SUVs and high-performance sedans); it has acceptable high and low viscosity ratings of “30” and “10,” respectively.

If your car’s engine typically gets so hot (maybe due to how you drive), a 10W30 oil may easily thin out and cause engine wear or overheating.

Talking of the 10W40 oil, this is typically the recommended motor oil for heavy-duty engines such as truck and motorhome engines. Notwithstanding, SUVs, sedans, coupes, and even convertibles can actually use 10W40 depending on temperature levels in the city where the car is often driven.

Put simply, the 10W40 oil is the thicker engine oil, and it’s the best choice for engines that do a lot of work or car owners living in regions with unusually high temperatures.

While a 10W30 oil may thin out in extreme conditions, a 10w40 oil would pull more resistance and protect the engine better because it has a higher tolerance for hotter temperatures.

When To Use 10W30 or 10W40?

Of course, there are conditions to decide if you should use 10w40 or 10w30 motor oils. If you live in an area where the temperature levels don’t exceed 30°C (86°F), it’s totally safe to run 10W30 throughout the year, and your car’s engine would work just fine – as long as you stick with a good oil, synthetics, preferably.

In contrast, if your city’s temperature exceeds 30oC, which means the temperature levels typically go above 100oF, it’d be advisable to run 10W40 all year until you leave that city.

It’s not bad to run 10W40 oils when you’re living in a city with normal temperature levels all year round, but 10W30 would just be better in such a case.

Both 10W30 and 10W40 would crank your car’s engine pretty fast in cold temps, and of course, they can come in full synthetic, synthetic blends, or conventional options. It is best to stick with the full synthetic options anyways because they offer more benefit to motor engines than blended or conventional oils.

However, your city’s temperature levels notwithstanding, if your car’s manufacturer says you should use 10W30 or 10W40 for the engine, it is best to stick with the OEM recommendation.

While using other oils (rather than what’s specified in your car’s owner’s manual) won’t hurt the engine, using the recommended oil would cause the engine to last longer and run more efficiently.

Frequently Asked Questions

Is It OK To Use 10W40 Instead of 10W30?

Yeah. Using 10W40 instead of 10W30 won’t hurt your engine. It’s very okay to use 10W40 instead of 10W30, especially if your vehicle is equipped with a heavy-duty engine or you live in a place where the temperature gets so high often.

What Is Better, 10W30 or 10W40?

The better option depends on where you live and what’s indicated in your car’s owner’s manual. If your car’s engine is specified to run with 10W30, apparently, that’s the better option, and if it’s specified for 10W40, that’s equally the better option. Notwithstanding, you can use these oils interchangeably in and out of seasons.

Should You Use Thicker Oil In An Older Engine?

Older engines require thicker (high viscosity) oils like 10W40 for optimal performance. It is advisable to use thicker oils in older, high-mileage engines. This prevents engine wear and ensures that the engine components continuously run smoothly.


Is 10W30 thicker than 10W40? No, 10W30 is lighter than 10W40 and would flow more easily in higher temperatures. On the other hand, 10W40 would better protect the engine in higher temperatures.

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