SAE 30 vs 10w40: What’s the Difference?

Motor oils come in a ton of different varieties and have a bunch of properties that cater to certain types of engines. When you walk into the hardware store it’s pretty easy to get overwhelmed with all of the options on the shelves. While asking for help to find what you need is pretty easy, it’s kind of nice to know how oils are labeled and rated, and what their benefits are.

When it comes to a comparison between SAE 30 vs 10w40, there are a handful of things to take into consideration. I’ll start with an overview of the two and then dig a little bit deeper into each of their characteristics and uses.

SAE 30 vs 10w40 (The Short Version)

In a word, the key difference between SAE 30 vs 10w40 is viscosity. SAE 30 is a medium thickness, single-grade oil that is mostly used in small engine machinery such as lawn mowers and string trimmers. 10w40 is an oil that is mostly used in diesel engines and motorcycles. This is because 10w40 is slightly thicker when hot, and also rated for use in cold temperatures.

Is SAE 30 the Same as 10w40?

SAE 30 is not the same as 10w40. SAE 30 is a pretty run-of-the-mill single grade oil. This means that it has been rated once at a high temperature. 10w40 oil, on the other hand, is a multi-grade oil. This means that it has been rated at very hot and very cold temperatures.

To answer the question: is SAE 30 the same as 10w40? You’ll need to understand the main physical differences between the two. The most important variables are temperature, and thickness/viscosity. In terms of temperature, both SAE 30 and 10w40 are rated at 100 degrees Celsius. They are then assigned a rating between 0 and 100 with lower numbers representing thinner oils and higher numbers representing thicker oils.

This is where the “30” in SAE 30 and the “40” in 10w40 come from. Knowing this, you can see that when hot, SAE 30 will be thinner/less viscous than 10w40. This is not the case in cold temperatures. 10w40 has additives that allow it to remain thin at very cold temperatures.

SAE 30 does not have these additives and will thicken at cold temperatures. If engine oil isn’t thin enough at low temperatures, it makes it difficult for engine parts to get proper lubrication before the engine is warmed.

The Characteristics of SAE 30 and Its Benefits

Widely known for its use in small engines, SAE 30 has a viscosity that sits right in the middle of the spectrum. As a single grade oil, you can’t expect any cold weather performance benefits from using SAE 30, but when it comes to lawn mowers you don’t really need them.

One benefit of using SAE 30 is that you can find it just about anywhere. On top of this, it’s usually one of the cheaper oils available. Paying extra for a multi-grade oil isn’t always the best option when it comes to your mower. Simple, warm-weather engines are the perfect fit for SAE 30 oils.

The Characteristics of 10w40 and Its Benefits

Since I’ve already touched on its uses a little bit, let’s break down 10w40’s meaning more literally. The “10w” part of 10w40 represents a rating of 10 during the winter (w). A rating of 10 suggests that 10w40 remains very thin at cold temperatures which is really important for engines that need to be started and run for a while before they are warmed up. The “40” part of 10w40 is the high-temperature rating. What this means is that when hot, 10w40 will behave the same as a regular SAE 40 oil would.

Because it is more adaptable to different temperatures, 10w40, and multi-grade oils in general, are used in some automobiles and other engines that need to run year-round. 10w40 also works well for older engines that may tend to leak or burn oil a little bit. With a higher viscosity, it can handle some abuse.

Frequently Asked Questions About These Oils

I’ll be the first to admit that it’s easy to get confused about the differences between oils when reading their code-like names. Even after knowing the key physical differences between engine oils, it can be tricky to know their uses. One of the most common questions I’ve noticed is, can I use 10w40 instead of SAE 30 in my lawn mower? Let’s talk a little bit about what oil is best for most lawn mowers, and when using 10w40 works well.

Can I Use 10w40 Instead of SAE 30 in My Lawn Mower?

Before I dig into this question, I should say that referencing your owner’s manual is the best way to find out what oil you should use in your lawn mower. However, in general, I probably wouldn’t recommend using 10w40 instead of SAE 30 in your lawn mower.

Most lawn mower engines are designed to use oil with a viscosity rating of 30. Because 10w40 has a higher viscosity, your engine might not be able to lubricate itself as easily. This could lead to strain and wear on engine parts. Unless your engine calls for 40 weight oil, or is older and tends to burn or leak oil often, 10w40 oil is probably a bit too thick for most mowers.

In addition to working harder, multi-grade oil could be seen as overkill. Even in the coldest parts of the country, most people aren’t going to be cutting grass in temperatures that would cause oil to thicken excessively.

With that being said, if you have a riding mower that you use to haul firewood or do other chores in the winter, multi-grade oil might be a great choice. But if your riding mower is rated for 30 weight oil, 10w30 would work better than 10w40.