When the time comes to purchase a new car, there are going to be a number of questions. One of them is 5w20 vs 5w30: which is better?
The formula of XwY in relation to automotive oils is centered around weight, and how smoothly the oil flows through the engine at different temperatures.
Let’s take a look at when 5w20 is preferable, when 5w30 is preferable, and what the driving factors are that make one better than the other in certain situations.
What is Viscosity?
Viscosisty is the name of the game when it comes to motor oil. Throughout this article, we will refer to this term frequently so let’s define it real quick before we get started:
vis·cos·i·ty: the state of being thick, sticky, and semifluid in consistency, due to internal friction. (Google dictionary).
In different temperature environments, oil will be less or more sticky, and will flow easier through the engine or with more work required.
5w20 vs 5w30: The basics
The ‘W’ in the equation stands for ‘Winter.’
The number before the ‘W’ is how heavy the oil is when it is in frigid or non-heated environments.
Cold climates, chilly seasons – this type of stuff affects the weight of the oil and how it flows through the engine.
Best synthetic oil 5w20 has a Winter rating of 5 and will function like a 20 weight oil with heat.
Back in the day when this equation for automotive oils was first generated, cars weren’t driven as heavily in the winter as they are now.
They didn’t have the four-wheel drive capabilities now common in many SUVs and other cars. As a result, it wasn’t nearly as common for winter viscosity to be a big deal to the driver.
Nowadays, drivers should be sure that they (or whoever is changing their oil) are using the recommended type.
To understand why this is so important, it is important to understand the basic formulas for engine oil.
The higher the number, the thicker the oil is.
This means that a 5w30 is NOT going to flow as smoothly as the 5w20.
When cool (after the engine has not been running for a while), they have a very similar viscosity. It is when heated and running that the difference is noticeable.
This means that the 5w30 oil has the same Winter rating, but functions as a 30 weight oil under heated conditions.
It is important to note that many vehicles will list a couple different acceptable viscosities for engine oil. In the short term, you won’t kill your engine by putting 5w30 in there instead of 5w20.
But still, it is important to know what your car needs and give it that whenever possible.
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5w20 vs 5w30: When Each Should Be Used
Which automotive oil is better for your car or truck depends largely on what type of climate you live in.
This can usually be found in the owner’s manual for the vehicle. Your car’s engine is built to function optimally on one specific viscosity.
Therefore, for longer engine life, better gas mileage, and less non-routine maintenance, you’ll want to use the oil that is specifically designed for your engine.
Many believe that 5w20 engine oil provides slightly better fuel economy. This is because there is less friction caused in the engine due to the thinness of the oil.
You’ll also get better lubrication when starting the car in the cold – meaning that the engine will have an easier time running right away and not stalling or hiccupping. However, the downside is that it is also believed to reduce the engine life by up to 30%.
In colder temperatures, engines function better on oil that will flow easier. This is why there is a lot of talk around 5w20 being better in colder climates. Down towards the equator, you’d be hard-pressed to even find 5w20 oil in a lot of places.
5w30 motor oil should be used when it is really hot outside. If you live in a place like Phoenix in the summertime, you’ll want the higher viscosity oil to keep the oil flowing smoothly through the engine even when the engine is above normal running temperature. Oil generally flows faster when heated up, so you won’t have as many problems with the thickness as you might in colder climates.
Mobil 1 5W-20 Synthetic
Mobil 1 5W-30 Synthetic
Sulfated Ash, wt%
HTHS Viscosity, mPa•s @ 150ºC
Pour Point, ºC
Flash Point, ºC
Viscosity @ 100ºC (212ºF)
Viscosity, @ 40ºC (104ºF)
Other things to consider
5w20 or 5w30: which is better?
What it really comes down to is two things: the owner’s manual recommendation and personal preference or risk factor.
A general rule of thumb is that 5w20 increases fuel efficiency in the short term, but causes added wear and tear on the engine. 5w30, on the other hand, helps the engine maintain high-performance functioning for a longer period of time, giving you as the driver more consistency and ultimately, peace of mind. If you don’t want to take the risk, go with 5w30.
Hopefully this article has given you a good background on 5w20 and 5w30, and which is better for your situation. Please share on your social media networks, and help us increase automotive awareness across the world.
If you have a certain make or model vehicle that you’d like to discuss, leave a comment below and we’ll get a friendly reader-driven conversation going.