6.0 Powerstroke 5W40 Vs 15W40: Key Differences

When buying engine oil for your truck or vehicle, one of the things to check is the viscosity of the oil. This is so important because using the wrong oil (which has a poor or higher viscosity) can affect the performance of your car’s engine.

6.0 Powerstroke is among the best and most reliable engines the market has to offer; if well maintained, the engine can last hundreds of thousands of miles without giving any issues. One of the ways to make a 6.0 Powerstroke engine last long is using the right, recommended oil.

A 6.0 Powerstroke can use 5W40 or 15W40 engine oils, but which among these two oil viscosities is best for your Powerstroke engine? What is the difference between 6.0 Powerstroke 5W40 vs 15W40?

Below is the most detailed comparison between these two motor oils that will help you know which of them is the best for your truck!

What is a 5W40 Oil?

5w40 is an engine with a dual viscosity rating for hot and cold temperatures, respectively. The “W” that separates the number represents “Winter,” while the numbers represent the viscosity rating of the selected oil in hot and cold conditions.

A 5W40 oil is a motor oil with a “5” viscosity rating for cold temperatures and a “40” viscosity rating for hot/normal operating temperatures. Viscosity refers to a fluid’s resistance to flow in specific temperatures.

So, a 5W40 motor oil would flow easily in low/cold/winter temperatures and put up some resistance (flow sluggishly) in high/hot/normal operating temperatures. 5W40 is usually fully synthetic oil and is recommended for most modern engines.

What is a 15W40 Oil?

15W40 is a motor oil that slows sluggishly in hot and cold temperatures. It is usually the ideal choice for heavy-duty engines that do a lot of work. This type of engine oil is best used in diesel engines, and it offers many benefits.

The 15W40 oil would drive well in the summer and winter seasons; however, you may experience difficulties starting your engine in extremely cold temperatures (freezing climate), usually during winter, due to its “15” viscosity rating in low temps.

The comparison of 5W40 and 15W40 is common among Ford Powerstroke owners. Well, both oils are slightly the same and slightly different; this is not to confuse you, but below is how they compare with each other.

6.0 Powerstroke 5W40 Vs 15W40

Oil Type/Comparison5W4015W40
Oil TypeFully syntheticConventional
ViscosityLess viscosity, thinner oilHigh viscosity, thicker oil
Best ForDriving in cold temperaturesDriving in a cold climate
Fuel EconomySaves more fuelNormal
PriceExpensiveCompetitively price

Oil Type

Most engine manufacturers strongly recommend using fully synthetic oils because they are made with refined base oils. That said, you’d usually see 5W40 recommended in your truck’s owner’s manual.

Notwithstanding 15W40 is practically the best-suitable oil for diesel Powerstroke engines, most people do not recommend it since it’s conventional oil. 5W40 is good if you’re going for fully synthetics, and 15W40 is the best if you use conventional oils.

Starting Time

During the summer season, a 5W40 would start your engine as fast as a 15W40 would do because both oils have the same viscosity for hot/high temperatures.

However, in freezing temperatures, the 5W40 would start a lot faster than the 15W40 because it is thinner and flows much more quickly in colder temperatures.

So, regarding the starting time, the significant difference between 5W40 and 15W40 depends on the season. If it’s the winter season, you will experience faster/easier starts with the 5W40 than you’d get with a 15W40. You may want to use 15W40 outside winter seasons and 5W40 when it’s winter again!

Drain Intervals

Actually, everyone has different suitable drain intervals; some drivers follow an annual drain interval, and others decide based on mileage. However, fully synthetic oils offer longer drain intervals than conventional and other motor oil types.

That said, 5W40 will most likely offer longer drain intervals than 15W40. But then, it is recommended to do an oil change between 10,000 and 12,000 miles to ensure the smooth performance of your Ford 6.0 Powerstroke.

With 15W40, you will have to do an oil change at least twice a year, but with 5W40, you’re safe with one oil change per year if you cover less than 15,000 miles annually. The decision is yours, right?

How To Choose Between 5W40 and 15W40

First things first, if you want to get the best from your 6.0 Powerstroke engine, you have to stick with the recommended oil in your owner’s manual. If the manual says 5W40, that’s the oil to go with.

Notwithstanding, from an expert’s point of view, and for people who always don’t care too much about OEM recommendations, choosing between 5W40 and 15W40 is seasonal. They are both good oils, but you should use 5W40 in cold climates and 15W40 in hot climates.

Frequently Asked Questions

5W40 and 15W40, Which Is Best For 6.0 Powerstroke?

Mechanically, both 5W40 and 15W40 would perform well in a 6.0 Powerstroke, especially if it’s the summer season. You should choose the 5W40 if you’re a fan of fully synthetic oils and the 15W40 if you do run conventional oils.

How Often Should You Change the Oil in 6.0 Powerstroke?

The official recommendation is to keep Powerstroke oil change at 5,000 miles intervals, but that’s too close for most people. You can drive up to 10k miles before an oil change if you use fully synthetic oils, but you should keep it at 7,500 miles maximum for conventional oils.

Can You Mix 5W40 and 15W40?

Yes, there is nothing wrong with mixing engine oils for your engine. However, when you mix two motor oils, you deprive your car’s engine of enjoying the full benefits each of the oils could offer individual. You can mix 5W40 and 15W40, but mixing motor oils is not advisable.


What’s up with this 6.0 Powerstroke 5W40 vs. 15W40 comparison? This article aims to explain the differences between these two common motor oils used by 6.0 Powerstroke owners.

Both are recommendable and deliver optimal performance at hot temperatures; the difference sets in when it’s winter or you move to a place with a constant low temperature. Regardless, stick with what you have in the owner’s manual if you want the best performance from your 6.0 Powerstroke.

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