Top 6 Best 15W-40 Diesel Oil

Ken

Updated: March 22, 2022

Oil Changes

Pretty much any diesel engine manufactured in the last few decades requires 15W-40 oil. This type of motor oil is able to lubricate and protect both low- and high-temperature engines, making it an ideal choice for a variety of climates. Not all 15W-40 oils are created equal, though; if you’re looking for the best protection for your diesel engine, you’ll want to make sure to choose a quality product.

In this article, we’ll take a look at top 6 of the best 15W-40 diesel oils on the market today. We’ll also give you a little bit of information about each one so that you can decide which one is right for you.​

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What Does 15W-40 Mean In Oil?

To the average consumer, these symbols are just numbers and letters – but they can mean a lot to people who have cars running on diesel engine oil. Depending on what kinds of vehicles you drive or cars your friends drive, you might already be familiar with the significance of 15W-40. If not, don’t worry! This article is here to walk you through the basics.

In oil, viscosity is one of two key factors that determine its function. The other factor is fuel type or “grade.” These two qualities work together to determine the oil’s ability to lubricate an engine and prevent overheating, which can ultimately cause a breakdown. For specific applications, you need a good viscosity and a good grade of oil to protect your engine. What does viscosity mean, though, and what is 15W-40?

Viscosity measures the ability of an oil to flow at a given temperature. If it doesn’t flow well, then you can have major problems with combustion inside your engine – that’s why you need a good flow of oil to keep everything safe. The “W” refers to winter and the “40” refers to the oil’s ability to lubricate at 40 degrees Fahrenheit. Those who drive in colder climates will want a high viscosity so that their engine can operate without overheating. If you don’t, your car won’t seem to run as well and you could lose power.

To choose the best 15W-40 oil for your car or truck, check out our top list below.

What Is 15W-40 Oil Used For?

Depending on the year, make and model of your car, you may need to use a specific viscosity (weight) for your vehicle’s oil. Regular motor oil typically has a weight that ranges between 0W-20 or 10W-30. However, if your owner’s manual calls for 15W-40 instead, then you should be able to find an oil of this weight to use in your car.

If you happen to own a car that requires 15W-40 oil, then it’s probably for one of two reasons: the engine is old, or the engine has high mileage (over 100,000 miles). The reason your owner’s manual calls for 15W-40 instead of 5W-30 or 10W-30 is because older cars need this type of oil to protect against moisture intrusion in the engine.

High performance vehicles benefit from this kind of oil as well, especially if they are “built” (modified) engines. The reason high performance vehicles call for 15W-40 is because this viscosity of oil can give them the performance they’re looking for.

Oil isn’t the only component of your car’s engine that changes as it gets older and gains more mileage, and therefore becomes less efficient. Many cars also need a thicker oil after 100,000 miles have been added to their odometer. Sulfur buildup on the piston rings is one of the main causes of oil thickening, and this happens to just about every car eventually.

As engine performance decreases, it’s always best to consult your owner’s manual rather than guess what viscosity weight you need to use in order to keep your car running smoothly. While most manufacturers recommend a specific weight, they’re usually within a range. This way you can use the oil that is appropriate for your vehicle year after year without having to be concerned about checking the manual every time you change it.

Best 15W-40 Diesel Oils

Types of 15W-40 Oils

A 15W-40 oil is an oil that has a viscosity of 15 centistokes when the oil is at 100°C (212°F), and 40 centistokes when the oil is cold. This type of viscosity is used most often in diesel engines because it allows for less wear on parts and more time between oil changes. There are three main types of 15W-40 diesel oils: synthetic, conventional, and blend.

Synthetic

Synthetic diesel oil has the advantages of better fuel economy, higher horsepower output for smaller engines, greater stresses on engine parts (such as increased compression), increased lubricity over longer periods, lower noise levels (viscosity-controlled hydrodynamic fluid film), less internal friction, and cleaner emissions. In addition, synthetic 15W-40 oils can reduce maintenance costs and fuel consumption due to better protection at start-up and better cold weather performance.

Conventional

Conventional diesel oil is made up of 80 percent petroleum base stock and 20 percent additives (detergents, antiwear agents, antioxidants, rust inhibitors, etc.). They are typically less expensive than synthetic oil.

Conventional 15W-40 diesel oils have advantages of better low-temperature fluidity, prevention of sludge formation, reduction in the proportion of pollutants during combustion, and being biodegradable. Additionally, it can be used as a crankcase lubricant. However, it is not as capable of protecting the engine against corrosion, which can lead to premature wear and damage.

Blend

Blend diesel oil is a mixture of petroleum-based 15W-40 diesel oil and synthetic or conventional oils; they are typically more expensive than conventional 15W-40 diesel oils. They offer advantages of better low-temperature fluidity, prevention of sludge formation, reduction in the proportion of pollutants during combustion, biodegradable, and being able to be used as a crankcase lubricant.

Additionally, they offer protection against corrosion which can lead to premature wear and damage. However, blend oil does not have the same capabilities of protecting engines against wear and damage as synthetic oil.

The best 15W-40 diesel oil is Shell Rotella T5 Triple Protection. This is the most popular of the diesel oil that use a 15W viscosity. Conventional motor oils are too thin for modern diesel engines. The best synthetic diesel oils have a high viscosity index, which protects the engine from damage due to heat and high-speed rotation of the crankshaft.

Choosing The Right 15W-40 Oil

When you are looking for a 15W-40 oil, there are many options to choose from. It is important to pick the right one not only due to the price but also because of its function. There are many oils that can serve as an alternative option. The purpose of this article will be to teach you what factors you should consider when shopping for a product.

Price

$7-10 per quart, depending on the brand

One of the factors you should consider when choosing an oil is its price. You need to purchase a 15W-40 that fits into your budget while still getting quality results. Since there are many different types of oils for this type of engine, the price may vary greatly depending on the brand and quality. The more advanced and high-quality an oil is, the higher it will be priced. Generally speaking, a reputable manufacturer will charge more for its products than a less popular one or a generic brand available at convenient stores or gas stations. Some oils can be found at your local store, such as Mobil 1 and Castrol oils, while others can be ordered online at Amazon or Ebay.

Brand

The brand of oil you choose plays a significant role in the quality and price of your product. Some brands offer their products in bulk which means that if you buy in larger quantities, the unit price will go down accordingly. However, if you end up using much more than expected, then this may not be beneficial for you since it may end up costing more than what you initially planned on spending. Additionally, compared to generic or no-name brands (e.g., Amsoil), well known and reputable manufacturers tend to come with higher prices; however, they usually provide better overall quality and better customer service.

Function

Protects against metal corrosion, helps in production of energy

Your 15W-40 oil should not only be able to provide you with the type of performance and quality that is advertised but it should also protect your engine from corroding due to metal damage. This will help prolong the life span of your machine. Additionally, when you purchase a 15W-40 oil that also functions as a lubricant; then this means that it doesn’t require you to add any other types of additives such as extra lube oil or grease for parts like bearings and gears (unless otherwise stated). However, if you have a machine with parts that require adding additional oil or, then make sure you factor the price of oil with add-ons when buying a product.

Customer Reviews

Positive 4.4/5 from over 500 reviews

You should also take into consideration what others have to say about the product that you are interested in purchasing before making a final decision. Not only will this help you learn more about your potential purchase but it might motivate you to buy a particular product even if its unit price is relatively high compared to other alternatives. Over 500 customers have taken their time and left their opinions on Amazon, many of which gave positive comments about this specific 15W-40 oil.

Based on the information above, you should now have a better understanding of what factors are important when determining which 15W-40 oil is best for your car.

Final Thoughts

While the best 15W-40 diesel oils are equal in terms of performance, some are better suited to certain applications. For example, if you drive an older or high-mileage vehicle, you can’t go wrong with Shell Rotella T5.

If you’ve got a new vehicle with a lot of miles on it, consider adding Shell Rotella to the oil at every oil change. This will put all the additives from the engine back into the oil and help prolong engine life.

Just like with regular vehicle engines, stay away from oils that advertise extended drain intervals. Just like in the early days of vehicle engines, this sounds good on paper but doesn’t work out so well in reality. Though heavy-duty diesel engine oils are much better than they used to be, they still need to be changed often enough that extended drain intervals are not necessary.