The Difference between 10w30 and 10w40 in Car Engine Oil

When your engine is running, it has oil circulating through its components. The purpose of oil is to lubricate and cool off these components. That way, they don’t overheat and suffer wear and tear damage. But you must put the right kind of oil in your engine if you want it to have the longest lifespan possible.

The difference between the various oil products on the market pertaining to their thickness and weight. The oils 10W30 and 10W40 are two common multi-grade oils which are represented by a first number, a “W,” and a second number after the “W.” Sometimes there are single grade oils which only have a “W” and a number after it. But with 10W30 and 10W40, they measure the oil’s thickness level.

The viscosity is what the first number represents. This determines the level of stickiness and thickness of the oil when it is subjected to colder temperatures. You’ll need to know this number if you live in a snowy or cold environment. It’ll determine how freely the oil can circulate throughout the engine as it is subjected to the cold.

Contrary to popular belief, the “W” does not stand for weight. It stands for winter because the temperature is everything when thinking about the thickness of your oil. Thicker oil flows better in warmer temperatures, and thinner oil flows better in colder temperatures.

For instance, a 10W oil is thicker than a 5W oil, so it is better to have 10W oil in hotter environments. The heat will reduce the thickness of the oil and create a smooth flow in the engine. But if you’re living in a colder environment, 10W oil will become too thick and cause the engine to perform more slowly. You’ll need a thinner oil like 5W in the cold because it’ll become just thick enough to flow steadily in the engine.

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Now let’s talk about the second number, which follows the “W.” This determines how well the oil flows in the engine when the temperature is hot. There are two ways in which oil can get hot. The most common way is from the hot temperature outside, especially during the summertime or in tropical locations. The second way is from the heat produced by the engine.

We’ll compare the differences between 10W30 and 10W40 engine oil so that you can better understand this.

10W30 Engine Oil

The “30” after the “W” means that this oil is more suitable for colder environments. In fact, if you want to lower the hot temperature of your car engine, you’ll want to have 10W30 flowing through it. In general, 10W30 is the standard oil used in the average car. But it doesn’t offer the best protection for the engine if the environmental temperatures change frequently. If you live in a northern state, then 10W30 might be better to use in the wintertime only.

10W40 Engine Oil

10W40 is like 10W30 because both have a “10” for their weight.  This also makes 10W40 suitable for colder environments too. However, the “40” after the “W” indicates that the oil can handle hotter engine temperatures. In other words, 10W40 gives your engine some extra protection against any possible overheating issues. It does this by sticking to the components of the engine and keeping them lubricated and safe from the wear and tear caused by friction. Therefore, the best time to use 10W40 would be if you live in a colder environment but are worried about your engine overheating.


The owner’s manual of your vehicle usually recommends the type of oil to use for it. However, the manufacturer doesn’t consider the temperature of the environment that you’re living in. Now that you have this information about the difference between 10W30 and 10W40, perhaps you can make a more informed decision as to which oil you’ll use for your engine.

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