Comparing 5W20 and 5W40 Engine Oils

Today we will be looking at 5W20 VS 5W40 engine oils to understand all the similarities and differences, and which type of oil you should choose.

But first things first, did you know that engine oils are graded according to many factors? One of those factors is the oil’s viscosity in relation to temperature.

The Society of Automobile Engineers(SAE) has assigned different values such as 5W20 and 5w40 to engine oils to represent the oils’ viscosity grades in relation to temperature.

If you come across an engine oil that is labeled “ 5W20” or “5W40”, here’s what you should know;

The number that appears immediately before the letter ‘W’(e.g 0, 5, 10, or 15) denotes the oil viscosity at 0°F or -17.7778°C. The lower it is, the better the oil’s performance at low temperatures, and vice versa.

On the other hand, the numbers that appear immediately after the letter ‘W’ (e.g 20, 30, 40, and 50)denote the oil viscosity at a high temperature of 212°F or 100°C.

The higher these digits are, the thicker the oil is and vice versa. The thicker or more viscous the oil is the better it will adhere to the engine’s components and the better it will protect it at high temperatures, and vice versa.


The only similarity between 5W20 and 5W40 engine oils is that both protect and safeguard the engine. Otherwise, these oils are very different in many core aspects.


  1. 5W20 is a relatively thin oil at very high temperatures whereas 5W40 oil is a relatively thick oil at the said temperatures. It’s also fairly viscous at lower temperatures.
  2. 5W20 engine oil is great for cold starts where you start the engine when it isn’t yet at its optimum temperature. 5W40 engine oil, on the other hand, is good for both cold starts and hot starts where you start the engine when it’s already overheated.
  3. 5W20 engine oils are good for both normal temperatures experienced in moderate climates and winter temperatures down to -31°F or -35 °C. 5W40 engine oils, on the other hand, are suitable for normal temperatures, higher temperatures up to 104°F(40 °C) and lower temperatures up to -31°F(-35 °C).
  4. 5W20 engine oils are suitable for low-performance and medium-performance(normal) engines that generate low or median temperatures. 5W40 engine oils, on the other hand, are good for high-performance engines that produce high heat.
  5. A 5W20 engine oil helps you save more fuel. On the other hand, a 5W40 engine oil doesn’t help you save as much gas.

As a side note, engine oils do have a direct impact on fuel consumption. When you use a low-viscosity engine oil like a 5W20 one, it reduces engine friction.

This enables the oil to flow more effectively through the engine, allowing the engine to work more efficiently while using less fuel. The opposite is true for high-viscosity engine oils like a 5W40 one.

Aspect5W20 Oil5W40 Oil
Viscosity at coldLow viscosity, flows easily at cold temperaturesHigher viscosity, takes more time to flow at cold temperatures
Viscosity at highCan break down at high temperaturesStable at high temperatures, can resist thermal breakdown better
Fuel economyProvides better fuel economySlightly lower fuel economy than 5W20 due to higher viscosity
Engine protectionMay not protect engine components effectivelyProvides better protection to engine components with higher anti-wear additives
Use for newer carsRecommended for newer cars with low mileageNot recommended for newer cars with low mileage as they require more protection
Use for older carsNot recommended for older cars with high mileageRecommended for older cars with high mileage as they require additional protection
Performance in extreme coldPerforms better in extreme cold weather and aids in quicker engine start-upSlower engine start-up in extreme cold weather due to higher viscosity
Performance in extreme heatMay not perform as well in extreme heat, may lead to engine wearPerforms better in extreme heat and provides better protection to the engine
PriceSlightly cheaper compared to 5W40Slightly more expensive compared to 5W20

What To Choose?

The answer depends mainly on two things;

Your environmental temperatures.

If you live in a hot area, it means that your engine will always exceed its normal operating temperatures. As such, you’ll need a 5W40 oil because it’s more viscous and hence more suitable for these temperatures than a 5W20 oil.

If you live in a cold area, it means that your engine will hardly overheat. So, you won’t necessarily need a more viscous oil like the 5W40 one to protect and get the most out of your engine.

In other words, less viscous engine oil like the 5W20 one would just do a great job. Lastly, if you live in an area where temperatures are normal, again, this oil would be sufficient.

Your engine type

If it’s a high-performance engine, you want to choose the heavy-duty 5W40 engine oil. But if it’s a low-performance or average-performance engine, you should go with the normal 5W20 engine oil.


5W40 engine oils are thicker and heavier. Therefore these oils are suitable for heavy-duty or high-performance engines that tend to overheat due to their huge amounts of power.

They are also good for vehicles operating in hotter areas where the engines tend to overheat.

5W20 engine oils, on the other hand, are thinner and lighter. That makes them suitable for standard engines that produce normal amounts of power and hardly exceed their operating temperature limits.

These oils are also ideal for vehicles operating in cold areas that experience lower temperatures not exceeding -31°F or -35 °C or areas with normal temperatures such that the engines do not exceed their optimum operating temperatures.

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