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Last Updated on February 6, 2022
To understand the differences between 5W-30 and 5W-20, you first have to understand what the numbers mean and, in turn, what that means for your engine (car or generator). Typically, the differences aren’t substantial, in terms of the properties of the oils, but they do make a difference.
What separate 5W-30 and 5W-20 is how the properties of the oil change at high temperatures. Notice that we didn’t say low temperatures, because that number is the first number in the oil type, and both of these oils share the number 5.
So how much of a difference does this all really make and can you put 5W-30 oil in a vehicle that calls for 5W-20? Would it harm your engine or render the vehicle completely undrivable?
Jump Right to: Differences between 5W20 vs 5W30
Understanding Motor Oil Numbers
The letter W is not some scientific or auto parts jargon for something that you would only find on the Table of Elements or in some mind blowing mathematical equation. It simply means, “winter.”
That is telling you that the number preceding the letter W is nothing more than an indication of how the oil reacts at low temperatures, or how its properties change. The last number—in this case, 20 and 30—is indicative of how the oil reacts to high temperatures or the maximum operating temperature of your engine.
That’s it; that’s the definition of the numbers, however, that’s not necessarily what they mean, because we both know that there are many other numbers when it comes to motor oil, such as 0W-20 or 10W-30.
So we know what they stand for but what do the numbers actually mean? The numbers tell you what the viscosity of the oil is at a vague temperature since the temperature is not defined in this string of numbers and one letter.
You can safely assume that the winter viscosity is anything below freezing, or 32°F/0°C and the two-digit number at the end is the viscosity of the oil at temperatures of 212°F/100°C. In terms of water, these are the freezing and boiling points.
The higher the number, the thicker the oil at these temperatures.
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You may think of viscosity in terms of how thick a fluid is, as in the difference between honey and water. What it means in terms of the the auto industry is more broadly defined by how fast something flows. Water will flow out of a spigot at a much faster rate than honey would.
The entire purpose of oil is to keep the metal parts of your engine from rubbing up against each other, which causes damage. Oil creates a barrier of lubrication between moving engine parts, keeping them from doing just that.
Once upon a time, oil thinned when heated and thickened when it got cold. Unfortunately, that’s a nightmare scenario when you are trying to crank up a car that’s been sitting in 15°F temperatures all night. That’s where additives come in.
Additives have completely changed how oil reacts during temperature extremes. Oil now acts thicker at a level of high heat and thinner at colder temperatures.
The lower the number preceding the W, the more the oil resists its natural tendency to thicken during the winter. The higher the last two digits, the more it resists thinning out when the temperatures are high.
So What’s the Difference Between 5W-20 and 5W-30?
Now that we know what the numbers mean and how oil reacts to different temperatures, we can truly answer the question and understand the answer. In terms of winter temperatures, both oil types act the same.
Main Differences Summarized:
- 5W20 Oil – At lower temperatures, this oil is truly “fluid,” making the task of starting a cold engine considerably easier. It may be used at temperatures ranging from -31°F to 77°F / -35°C to +25°C (outside temperature). It’s more fuel-efficient, has a quicker flow rate, and is better suited to colder areas.
- 5W30 Oil – At lower temperatures, the viscosity of this oil remains the same. It is, however, somewhat thicker than 5W20 at higher temperatures. It may be used at temperatures ranging from -31°F to 95°F / -35°C to +35°C (outside temperature). It’s thicker, uses less fuel, and is better suited to a hotter climate.
|Low Temperature||Fluid||Thicker at higher temperatures compared to the 5W20|
|Recommended Use||-31°F up to 77°F / -35°C up to +25°C (outside temperature)||-31°F up to 95°F / -35°C up to +35°C|
|Key Differences||1. It’s more fuel-efficient|
2. Faster flowing
3. Suitable for colder climates
|1. Less fuel-efficient|
3. Suitable for warmer climates
|Where To Buy||Available on Amazon||Available on Amazon|
However, at higher temperatures, 5W-30 is more resistant to thinning than 5W-20. Let’s say you purchase a 2022 GMC Acadia in Wisconsin. Its likely that the oil recommendation will be 5W-20. However, if you move to Florida, don’t think that you can’t change that.
In fact, you can use a different range of oils in many vehicles, we’re just using the Acadia as an example. In Florida, it wouldn’t harm your Acadia to switch over to 5W-30, because the temperatures are consistently much warmer and for longer periods of time.
If you live in the Florida Keys, such as Marathon or Key West, 10W-30 isn’t going to break your Acadia’s engine and simply makes more sense to use than 5W-20. You’re engine is going to be warm almost all of the time, when 95°F is the norm and winter is 80° and windy.
What Changes When You Go from Conventional Motor Oil to Synthetic?
The changes are surprisingly subtle. Conventional oil does what it does based on the additives that are mixed in along with the specific properties of the motor oil on its own. Synthetic oil is a designed oil that attempts to mimic what conventional oil does, only better.
As time goes on, conventional oil breaks down and sheds the additives that are designed to make it do what it does, such as remain thin in the winter and fight to remain thick during the summer.
As it breaks down, it returns to what it was before the additives were put in, which is why 3,000 to 5,000 miles is the effective and practical limit of conventional oil, whether it is 5W-20 or 5W-30.
Synthetic oil is specifically designed to last much longer by not shedding the efficacy of the additives over time. This is why synthetic oil can go much longer in an engine before it needs to be changed.
The differences between 5W-20 synthetic oil and 5W-30 synthetic oil are the same as they were in conventional oils, however, the only difference is the fact that the synthetic version of both oils is designed to last longer.
Can You Mix 5W-20 and 5W-30?
You can definitely mix 5W-20 and 5W-30, however, there are some caveats, not to mention the fact that there is really no advantage or positive reason for mixing the two. The only exception would be for topping off you oil and you simply have one and not the other.
If you have to do it, you should always try and stick to the same brand, not including mixing synthetic and conventional oils out of the same brand. Its probably not going to do any harm, especially not if its a one-time thing.
However, mixing different brands runs the risk of mixing different additives that may or may not have a negative reaction to one another. Quaker State may use different additives than Mobil 1.
Frequently Asked Questions
The first number and letter (XW) indicates the viscosity of the oil in cold weather while the second set of numbers, preceded by a dash (XX) indicate the viscosity of the oil when temperatures are hot.
Yes you can. Not only can you do it, but its probably a better choice to go with a lower weight when regular temperatures are not hot in your climate. 5W-20 is really designed for cooler weather on average. Using it in hot weather will increase friction with the moving parts in your engine.
You can, but you’re getting into a more drastic difference in oil viscosity for both warmer and cooler temperatures. If you do it consistently, you will shorten your engine life, as the engine is designed for lower viscosity and the thicker stuff will be more difficult to move within your engine.
Is thicker oil better for high mileage engines?
It is better for high mileage engines because the side-effect of using thicker oil is that you create more oil pressure, pressure that is lost over time as engine parts wear down and you have slow oil leaks.
Is it ok to use synthetic oil in a high mileage engine?
Its not only ok, but its also highly recommended. Many people assume that synthetic oil is slicker and viscosity is lower, so putting it in a high mileage engine would be worse. This is false. If you have slow oil leaks, they won’t be exacerbated by switching to synthetic.
Synthetic is a purer oil that is formulated using natural gas. It burns cleaner and protects better and for longer periods of time than conventional oil.
Can I mix synthetic oil with conventional oil?
You can mix the two, however, you won’t get any additional benefits by doing so. The conventional oil will simply dilute the additional benefits of the synthetic oil, rendering those benefits negligible.
Can I mix 5W-20 with 5W-30?
You can but its not going todo anything additional for your car. Something like this is really only necessary if you need to top off oil or something along those lines. You should never make it a habit to mix the two oils.
There’s really no versus here so much as there is a comparison between 5W-20 and 5W-30. One is simply thicker than the other and both are useful in the vehicles that they are recommended for and in different climates.