The world of motor oil can get a little confusing if you're not sure what everything means. Every kind of motor oil has a rating on the bottle to let you know what kind of oil it is and, in turn, whether it's the right kind of oil for your car. Some of the most common oil ratings you'll see are 5w20 and 5w30. Taken as they are those numbers really don't mean a lot and if you're not familiar with how oil is rated then it's essentially just a meaningless mix of numbers with a letter.
Oil ratings are used to indicate oil viscosity. The viscosity rating is determined by the oil’s resistance to flow at a given temperature. The higher the viscosity, the thicker the oil is going to be. That means that flows less easily through your engine. Some engines need a lower viscosity oil, and especially in cold weather you need to have a lower viscosity because you still need the oil to flow through the engine rather than thickening up to an almost jelly like state. However, in high heat you want a higher viscosity so that it doesn't thin out until it's almost like water and it's not able to do its job properly.
When you see a motor oil like 5w20 or 5w30 that is what is known as a multi grade motor oil. The number before the W and the number after the W refer to different viscosity ratings. The W stands for winter. It's used to tell you the viscosity rating of the motor oil in cold weather conditions. So the first number, before the W, is the winter or cold weather rating for the oil. The second number, after the W, is the viscosity rating for the oil in normal operating conditions or warm weather.
In the case of 5w20 motor oil and 5w30 motor oil you can see that they both have a cold-weather rating of 5. This means that both of them perform exactly the same in cold weather conditions.
The second numbers, the 20 and 30, refer to the warm viscosity. The higher the number, the higher the viscosity. So 5w30 motor oil will be thicker at operating temperatures than 5w20 motor oil will.
How is 5w20 Different From 5w30 at Operating Temperature?
At 100 degrees Celsius, 5w30 is going to be slightly more viscous than the 5w20. Because 5w30 is thicker you are going to get a slightly lower fuel economy and slightly less horsepower out of your engine than you would with 5w20.
Because 5w20 oil is less viscous, it causes less drag throughout your entire engine. That means all of the moving parts are able to move around a little bit easier because they have less resistance from the thickness of the motor oil. That's why you get slightly improved fuel economy when you use 5w20 vs 5w30. The difference is very minimal however, and you likely wouldn't notice much of a change in fuel economy from one fill up to the next. Over the course of the year however, you may save a few dollars. That said, if your engine is not meant to use 5w20 then it would not be a good idea to try to use it just to save money at the gas pumps.
What Happens if You Use 5w30 Instead of 5w20?
You can use 5w30 instead of 5w20 if your engine allows for it. Some engines can safely use both kinds of oil and it will be mentioned in your owner's manual if that's the case. if your engine is not designed to use both weights of motor oil then you are putting the engine at risk if you take 5w30 instead of the 5w20 that it was formulated for. That's just because the components will not be able to operate as smoothly as they should because the oil going through your engine is slightly thicker which is going to force all of the components to work harder to perform their duties. This is why it's important to always check your owner's manual before adding any kind of new fluid to your vehicle, just in case.
Can You Mix 5w20 and 5w30?
In many vehicles you can use one kind of oil instead of the other, you can even mix both 5w20 and 5w30 motor oil if your engine allows for it. If you check your owner's manual and it states that you can use either 5w30 or 5w20, then topping one kind up with the other shouldn't cause any particular damage to the performance of your engine overall.
However, as we mentioned previously, if your engine is not suited for 5w30, for instance, you shouldn't be mixing that with your 5w20. You could cause your engine to struggle harder to perform and that will cause many of the components inside it to wear down that much sooner, potentially leading to some serious engine damage.
Keep in mind that it's possible you could void your warranty if you use the wrong kind of oil in your engine while your car is still under warranty. That's why checking the owner's manual is so important before you do anything like this.
Is 5w20 Oil Thicker Than 5w30?
As we said, the number after the W refers to the viscosity of the oil at a higher temperature. That means the lower the W number, the lower the viscosity or thickness of the oil. So, when you are actively using these motor oils 5w20 is going to be thinner when it's operating at normal temperatures and 5w30 is actually going to be the thicker oil when it's in your engine.
Is 5w20 Oil Good for High Mileage?
When it comes to the kind of oil that's going to be best for your car, the owner's manual is always the best way to go. If your vehicle recommends 5w20 oil, then that is definitely going to be the best option for you regardless of how much driving you do. Because your engine was specifically designed to handle that formulation. Switching from one formulation to another in an effort to improve mileage or improve your car's ability to handle a certain mileage isn't going to be a good idea. If the manufacturer recommends 5w20, then you should stick with 5w20. If they recommend 5w30, stick with 5w30. Of course there are a number of potential different oils you can buy, as well as some that claim to include additives that will help improve performance when your car is reached high miles but that's not necessarily something you need to be worried about.
If you are interested in any kind of oil that claims to improve performance at high mileage, just make sure you're doing your research ahead of time on the specific brand and formulation to ensure that it does work with your engine. When in doubt, always trust your owner's manual.
What Happens if I Use the Wrong Kind of Oil in My Car?
If your engine is designed for 5w20 motor oil and you use 5w30 instead, you may notice an increase in the oil leaks as a result. Every part of your engine was designed specifically to operate under the conditions outlined in your owner's manual. If the manual states that you specifically need to use one kind of motor oil and not another, then you risk damage as a result. There are a few signs and symptoms that you can be on the lookout for to let you know you may have put the wrong kind of oil in your vehicle. These include things such as:
Engine Noise: If you use the wrong kind of oil it's possible that your engine will sound louder than you're used to, and may even produce some kinds of ticking or knocking sounds that are not normal. This is because if you're using the wrong kind of oil it's causing all the parts to struggle a little bit more to get the job done. Consider it like trying to swim through Jell-O instead of trying to swim through water. You're going to have to struggle a little bit to get the same distance.
Oil Spots: If your oil is too thick or too thin for the way your engine is meant to operate, it may end up leaking from various valves, gaskets, and other parts of your engine. It shouldn't be a profound oil leak by any means, but you may see a few drops of oil on the driveway or in your garage that you're not used to seeing below your car.
Burning Smell: The wrong weight of oil will not be able to properly lubricate all the parts in your engine. If that happens, you're going to not only lose lubrication you're going to increase friction. That can lead to a burning smell because the oil that is present is not able to handle the job of keeping your entire engine properly lubricated. If you notice the smell of burning oil, or you're seeing any smoke coming from the engine, you definitely need to stop your vehicle right away as soon as it's safe to do so, and get your car into a mechanic.
Bad Fuel Economy: As we said, the difference between 5w20 and 5w30 can have a bit of an effect on your fuel economy overall. If you're using the 5w30 when you should be using the 5w20, that's going to cause your engine to work harder and your engine can only do that by burning more fuel. That's why you'll end up heading to the pumps more often as a result. It may not be a significant amount, but especially over a long enough period of time you'll start to notice you're leaving to gas up more often than you used to.
Should You Worry If You Use the Wrong Kind of Oil?
If you've realized you used the wrong kind of oil, you put in 5w30 when you should be using 5w20, then you don't need to panic too much. Even if your engine isn't specifically designed to use the other kind of oil, the damage you're going to cause between now and when you need to have your oil changed next is probably not very significant. If you're worried, then you can go get an oil change and have the right oil used instead. You're very unlikely to cause any noticeable damage over the course of a few days or even a few weeks using the wrong kind of oil. You just don't want to be consistently using the wrong kind of oil if you know for a fact that your car is not designed to be using it. It's possible you can even go in till your next scheduled oil change with the wrong kind of oil and suffer very little damage as a result. The difference between 5w20 and 5w30 is fairly minimal after all.
just to be on the safe side, if you do realize you put the wrong kind of oil in and your owner's manual specifies that you can't be using it, get your oil changed whenever it's convenient for you to do so and there should be no problems that you need to worry about.
The Bottom Line
It's been said more than once that oil is the lifeblood of a car. There's a reason that there are so many businesses around town that do little else besides changing oil. It really is one of the most important things to take care of if you want to keep your car running smoothly. That's why it's important to know exactly what kind of oil your car takes, and why it takes that kind of oil. Understanding the weight of the oil that your car needs and what the numbers mean helps you better understand how your engine works. That in turn means it's easier for you to buy the stuff you need to keep your car running smoothly and ensuring you avoid problems down the road if something goes wrong.