6.0 Powerstroke 5W40 Vs 15W40 Engine Oil: Which One is Better?

5W40 and 15W40 are the two most popular oil rating choices for 6.0 Powerstroke engines. 6.0 Powerstroke 5W40 and 15W40 is a common debate as they have slight differences, which give each of them an edge in certain scenarios.

Factors like weather, protection, price, and fuel economy are your main concern when deciding on the right oil for your truck. 

In this article, I’ll mention where each type of oil shines, also how engine oil rating works and what factors to look out for. Let’s dive in.

6.0 Powerstroke 5W-40 Vs 15W-40: At a Glance Comparison Table

Viscosity5 at 0o C and 40 at high operating temperatures (180-185o F)15 at 0o C and 40 at high operating temperatures (180-185o F)
Operating Range-35o C to 40o C-25o C to 40o C
Engine TypeBoth Petrol and DieselDiesel
AdditiveZinc and PhosphorusZinc and Phosphorus

Check More: High Pressure Oil Pump Failure Symptoms on 6.0 Powerstroke Engine.

Engine Oil Rating and Viscosity

If you’re not familiar with engine oil ratings, the numbers can seem pretty confusing. What the rating actually contains is just the viscosity value of the oil at two different conditions.

Engine oil’s viscosity indicates how thick or thin the oil is and how it behaves under different temperature conditions.

For multi-viscosity engine oils, viscosity is typically denoted by two numbers, such as 5W-30 or 10W-40, where the “W” stands for winter.This rating is provided by the Society of Automotive Engineers or SAE in short.

According to SAE, the first number (e.g., 5W or 10W) represents the oil’s viscosity at low temperatures, specifically during cold starts. The value is specific to 0o temperature.

On the other hand, the second number (e.g., 30 or 40) represents the oil’s viscosity at higher temperatures. It measures the oil’s resistance to flow when the engine is operating at normal operating temperatures.

A low viscosity value means that the oil is thinner, so it flows more easily in cold weather, providing better lubrication during startup.

In comparison, a higher number denotes a thicker oil that maintains its viscosity and provides sufficient lubrication under high-temperature conditions.

This actually denotes the main difference between the 5W40 and 15W40 oil variants. We’ll discuss it in detail in the next section.

6.0 Powerstroke 5W40 Vs 15W40 Main Difference – Cold Temperature Lubrication

The main deciding factor of these two types of oil, 5W40 and 15W40, is actually the oil viscosity or thickness. You can see that both oils have the same viscosity value for operating condition. 

This means that at engine operating temperature, both oils will offer the same thickness of lubrication. The colder temperature viscosity is where they differ from each other.

If you think of the viscosity value as a measurement of flow resistance, you can easily assess the comparative thickness between the two products.

As the 5W40-rated oil has a higher cold temperature flow, it is generally thinner than the 15W40-rated oil.

And for colder temperatures, you’d want the oil that flows more easily for better engine protection, faster lubrication, and less resistance.

Oil, like every other material, expands when heated and shrinks in colder temperatures. As engine oil’s main focus is lubricating the components, whichever oil can maintain runnier consistency in colder temperatures will provide quicker and better lubrication to the engine.

Also, a thinner oil is more effortless and quicker to lift, pump, and send to various components. It can also reach the narrowest gaps and slits of different components. 

These sides surely make the 5W40-rated oil a better lubricating option for Powerstroke 6.0 than 15W40 oil for colder starts.

Other Factors of Comparison – 5W40 Vs 15W40

Besides low-temperature performance, there are several other important criteria where the difference between these two oils can help you determine which oil you should get. Let’s take a look.

1. High Temperature Performance

Although 5W40 is thinner at lower temperatures, its rate of expansion with heat is greater compared to 15W40.

A greater expansion rate means that over the operating temperature, the 5W40 oil will lose its viscosity quicker than the 15W40 oil. This makes the 15W40 a slightly safer choice only in extreme engine temperatures.

If you’re involved in heavy-duty applications and off-road activities, the engine temperature can cross the optimum operating temperature very easily. While the 5W40 can provide good lubrication in such scenarios, the 15W40 will be a slightly more reliable choice for sure.

2. Fuel Economy

A thinner engine oil is more economical as long as it can properly lubricate all the A thinner consistency oil is also easier to pump and transport to places. Less resistance indicated less energy consumption and, therefore, better fuel efficiency.

Also, the engine can provide the best performance when it’s running seamlessly with the utmost lubrication. That’s because friction within components and surfaces makes the engine lose a good amount of energy. Therefore, poor lubrication results in poor fuel economy.

In that context, the 5W40 oil is definitely a more economical choice for lower temperature operations. The 15W40 oil can’t provide the same lubrication and fluidity at colder temperatures, and the lower the temperature drops, the worse its performance will get.

At higher temperatures, both oils have the same consistency, and therefore it won’t make any difference in terms of efficiency.

3. Protection from Wear and Tear

The purpose of lubricating engine components is to eliminate the wear and tear from constant collisions and friction. In a general sense, thicker engine oil provides better engine protection from friction.

But that is not true for colder temperatures. At colder temperatures, engine oils get thicker, which makes them harder to reach all components through narrow slits and gaps.

The bottom line is you want your engine oil thick, but not too thick. For 6.0 Powerstroke, the 5W40 provides superior lubrication at colder temperatures making it the better choice against constant wear in cold conditions.

4. Oil Longevity

A thicker oil is said to have more prolonged longevity. It’s mainly because more viscosity allows the oil to sustain heat damage. On the other hand, engine oil mostly loses its quality when it’s exposed to extreme heat.

So, if you’re driving in extremely hot weather or are involved in activities that put a good amount of pressure on the engine, the 15W40 oil would be a better lasting option for you.

But this doesn’t matter much for lower temperature operations. For colder operations, the 15W40 gets a negligible advantage which is easily outweighed by the massive benefit of the 5W40.

How Often Should You Change the Oil in 6.0 Powerstroke?

The oil change interval depends on factors such as driving conditions, mileage, and the type of oil used.

It is advisable to follow the manufacturer’s recommendations outlined in your vehicle’s manual. Typically, for 6.0 Powerstroke engines, oil changes are recommended every 5,000 to 7,500 miles or every 6 months, whichever comes first.


Are there any disadvantages to using 5W-40 oil in a 6.0 Powerstroke?

5W40 oil may be slightly more expensive compared to 15W40. Additionally, in certain operating conditions or climates where the engine runs consistently over high operating temperatures, a higher thickness retaining oil, like the 15W40, will offer better protection.

Can I switch from using 15W40 oil to 5W40 oil in my 6.0 Powerstroke?

Yes, switching between different viscosity grades is generally safe as long as the new oil meets the required specifications and recommendations for your engine.

Can I mix 5W40 and 15W40 oils in my engine?

Mixing oils can alter their performance characteristics, potentially affecting lubrication properties and engine protection.


Choosing the right engine oil is absolutely crucial for ensuring the betterment and longevity of your engine. So, which would be the better choice for your 6.0 Powerstroke 5W40 vs 15W40?

In short, the 5w40 would be an absolute winner when it comes to performance in low temperature settings. But if your vehicle takes extra loads and runs in higher temperatures most of the time, then the 15W40 would be a more reliable choice.

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