Reviews

Best Diesel Oils: Keep Your Vehicle’s Engine in Peak Condition

Boost your engine’s performance and keep your vehicle running smoothly with these best diesel oils.

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BY Corrina Murdoch / LAST UPDATED ON June 16, 2019

Engine performance is essential to your vehicle's overall performance yet needs proper care and nourishment to do its job. By choosing the best diesel oil for your truck, you're taking active steps to improve performance and assist in overall vehicle wellbeing. Not to be confused with standard motor oil, diesel engine oil features a higher part per million of additives than other options. Since diesel engines are more prone to generating soot and byproducts from combustion, getting oil to treat that wear is essential.

Of course, not all diesel oil is made alike. In the century-and-a-half since its invention, countless manufacturers across the globe moved to innovate the formula. The key to success is finding the best diesel oil for your truck and the road conditions you'll most likely face. To assist, we've broken down the best diesel oils available on the market today.

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All of our reviews are based on market research, expert input, or practical experience with most products we include. This way, we offer genuine, accurate guides to help you find the best picks.

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Benefits of Diesel Oil

  • Extend engine life. Diesel oil is formulated to have a high degree of natural solvency, meaning it can clean and remove deposits. This helps remove sludge and gunk from your motor, so it will run as smoothly and efficiently as possible, as well as extend the lifespan of engine seals and other components that make up the engine.
  • Maximize engine performance. Diesel oil is outfitted to boost the power of your engine, especially when it comes to hauling heavy loads or pulling a trailer. The fluid allows the engine to run more smoothly and more powerfully by removing blocked gunk or debris.
  • Improve fuel mileage. The best diesel motor oil will improve the amount of friction between key engine components, making your engine run smoother and more efficient. This also may increase the diesel fuel mileage of your vehicle, so you’ll spend more time on the road and less time and cash at the pump.
  • Increase the time between oil changes. Diesel engines are more robust and can handle a higher degree of power. Depending on the vehicle and motor oil used, diesel oil can even extend the time between your next oil change. That means you can spend more time on the road and less cash on swapping out the oil.

Types of Diesel Oil

Synthetic Oil

This type of artificially manufactured diesel oil consists of a set of synthesized base oils mixed with additives. The extra chemicals add to the diesel oil’s hydrophobic nature (water-resistance) and help emulsify debris. With detergents to molecularly scrub away debris, it results in cleaner, more efficient combustion.

Depending on the manufacturer, the synthetic oil will feature different additive blends. Many companies like Valvoline and Royal Purple have patents on their proprietary formulas, adding to the benefits of the pure nature of synthetic oil. Since there is no crude oil in the formula, this type has less debris and tends to result in slower wear.

Conventional Oil

Back in the day, all diesel oils were conventionally generated. This means that the formula relied on natural ingredients, namely mineral oil. The source of this type of diesel lubricant is crude oil. Because it is naturally sourced, there is less molecular consistency throughout the fluid. Due to this diminished ability to regulate the oil contents, the diesel industry has largely moved away from conventional oil.

Despite this downturn in popularity, you can still find mineral oil for diesel rides, such as the BRP Ski-Doo Mineral Oil. You're most likely to use this type for off-roading vehicles. It has some chemical imperfections but is extremely affordable.

Hybrid Formula Oil

Second to the full synthetic formula, hybrid diesel oil is the most common on the market. It consists of a blend of conventional and synthetic ingredients, offering the benefits of both. These solutions provide a fix for some of the downsides of synthetic oils. For one, they are more affordable to source, given that the materials for artificial chemicals are at least double the cost of natural options.

The additives in synthetic formulas can separate if left on the shelf, and the natural movement of the crude oil molecules mitigates this. Plus, when appropriately combined, this type of formula can optimize fuel economy. As a direct result of viscosity control through thermal resistance, this type of oil is well-suited to colder climates.

Top Brands

Mobil 1

Entering the industrial lubricant scene in 1974, Mobil 1 gained much recognition through its affiliations — namely the one it retains with NASCAR and Formula One racing. Tending to be one of the more trusted brands for luxury vehicles, mechanics often opt for this brand when dealing with anything from a Lexus to a Ferrari. Showcasing its benefits on a large scale through its market prevalence, everyday drivers reap benefits with products like the Mobil 1 Synthetic Motor Oil 0W-40.

Castrol

World-famous for its track record dating back to 1899, this company's namesake is a shout-out to the first people to put castor oil in an engine lubricant formula. It is based out of the United Kingdom, creating a wide range of lubricants for all vehicles. It's gained a good reputation for functionality and is favored by millions of people worldwide for quality and performance value. Among its top offerings for diesel engines is the Castrol Conventional Diesel Motor Oil, an effective go-to for 15W40 needs.

Liqui Moly

A German manufacturer of lubricants, as well as the base materials used in the formulas, Liqui Moly offers premium products that are ideal for demanding road conditions. Despite this, it remains a more cost-effective selection than other manufacturers, mainly in part to the streamlined supply chain of creating the ingredients for the formula and the final product in the same place. You can benefit from this convenience with the Liqui Moly Synthetic Motor Oil.

Royal Purple

One of the youngest companies in this industry, Royal Purple is a proudly American company that focuses on supplying lubricants for all vehicle types. Known for its diverse selection, it offers everything from marine engine treatments to motor oil for diesel engines. It’s grown popular with the racing community, facilitated through various sponsorship agreements like its arrangement with Formula DRIFT. The same products those racers use are available on shelves (both literal and virtual), with the Royal Purple 15W-40 Oil being a leading contender for diesel rides.

Valvoline

Just about every driver knows the Valvoline name, given its status as a global leader in premium automotive lubricants. Since its establishment in 1866, this Kentucky-based company has expanded sales to over 140 countries. For those driving a diesel rig and looking for the proven results for which this brand is famed, the Valvoline Premium Blue Synthetic Oil is a good pick.

Diesel Oil Pricing

  • Under $20: Less expensive motor oils tend to be conventional oil or synthetic blends. Synthetic blends are a good choice if you want some of the benefits of full synthetic oil but don't want to spend too much money. You also pay for the size and type of container, like gallons, quarts, or liters.
  • $20 and up: Full synthetic motor oils vary in price, and it's helpful to find the product on sale if you want a good deal. Some can be as cheap as $25, while others can be found starting at $60 and ranging to hundreds of dollars. You’ll get into the upper pricing section when buying in bulk as well.

Key Features

Viscosity

The viscosity grade is one of the most important factors in selecting the right diesel motor oil. Several factors are figured into the viscosity of a vehicle. Diesel engines are commonly rated between 15W-40 and 5W-40. The number before the W indicates the thickness of the oil when it is cold, while the number after is the thickness of oil at normal operating temperatures.

Application

The labels on all types of diesel oil list the specific application that the oil is designed for. Some common oil applications include higher mileage, extended performance, gasoline engines, and motorcycles. Do your homework on your vehicle’s condition before you purchase the best diesel oil for your needs.

Additives

Each diesel motor oil brand adds its own proprietary blend of additives to enhance certain properties. For instance, viscosity-index improvers work extremely well in ensuring that oil doesn’t get too thin at higher temperatures. Other additives like detergents are efficient cleaning agents designed to remove deposits and sludge from your engine. Determine which additives would provide the benefits you need the most before purchasing a synthetic engine oil.

Other Considerations

  • Diesel Oil Compatibility. The first consideration (once you know the oil will work with your diesel engine) is to think about the oil already in place. Most diesel oils will specify whether they are compatible with synthetic, hybrid, or conventional oils. The vast majority of diesel oils are made to work with all different types. Synthetic oils tend to have the highest compatibility rating, working with both old and new vehicles. Check the owner’s manual against the chemical specs to make sure you’re getting the best diesel oil. 
  • Road Conditions. Once you’re sure the oil will work with your ride, you can move on to consider the terrain on which you’ll be driving. Depending on the demand placed on your vehicle, the diesel engine will be more vulnerable to wear. The more intense the driving situations, the better the quality of the oil must be.
  • Quantity and Shelf Life. Except for the occasional full-scale oil change, you’ll need some top-ups. That means you’ll have a container of diesel oil that’s been opened and left on the shelf. Like everything else, it loses potency as it sits on the shelf. The chemicals can separate and interact with ambient heat for air introduced to the container. To optimize the utility of your oil, be sure that you get something in an opaque container with a good seal and choose quantities that match your needs.
  • Climate and Environment. The demands placed on your diesel engine differ based on ambient conditions. Cold causes oil to thicken, while heat causes it to thin. More humidity in the air means added risk of oxidation. Increased pollution means added likelihood of particulate in your diesel system. Consider the trials your engine must face and aim to find the best diesel oil to make those tasks easier.

Best Diesel Oil Reviews & Recommendations 2021

Best Overall
Royal Purple 15W-40 Oil

An entirely synthetic motor oil, the Royal Purple 15W-40 Oil formula is made primarily out of high-grade base lubricants. The chemical makeup of this motor oil is strengthened through these additives, facilitating added efficiency. Despite being tough on particulates, it won’t compromise the hardware in the vehicle. Effective on both gasoline and diesel engines, it’s a safe go-to solution. You can get the same formula in a range of viscosities, letting you find something compatible with your vehicle. It stands out as a selection that won’t cause issues when interacting with either a synthetic or conventional lubricant. The chemical stands out as an option that is tough in the right ways (descaling and cleaning) while remaining gentle where it counts.


It’s worth noting that the official recommendation of Royal Purple is to wait until the first scheduled oil change as the best time to introduce this diesel oil. If you add it too early, the positive effects of diesel oil are limited.

Best Value
Shell Rotella T6 Synthetic Diesel Motor Oil 5W-40 CJ-4

This heavy-duty synthetic diesel motor oil provides great protection and cleanliness to your vehicle’s engine. It doubles as a gasoline oil as well, acting as a bonus for anyone who may own diesel-engine and gasoline-powered vehicles. The improved wear performance provides a significantly increased level of protection against harmful engine wear.


The viscosity of this diesel oil doesn’t vary by much, even in the cold or heat. The added compounds of Shell’s Triple Protection Plus technology protect against soot, dirt, and other debris from building up. They also give your engine more power and boost its capabilities when needing to haul a heavy load or pull a boat for a day at the lake. Combined, this oil is designed to help you save money, time, and fuel consumption on the road.


Although affordable and effective, this engine oil is far from perfect: its 5W-30 design is suitable for the cold but not excellent for extremely hot environments. If you spend more time with AC than a heater, this oil may become too thin for your climate.

Honorable Mention
<strong>Mobil 1 Synthetic Motor Oil 0W-40</strong>

Mobil’s 0W-40 brand of diesel motor oil works hard to protect, lubricate, and boost a vehicle’s performance while preventing leaks and keeping critical engine parts in working order. It works hard to make sure your vehicle works like new again to give you peace of mind on the road.


It’s advanced, fully synthetic formula prolongs the life of your vehicle’s engine and blocks the buildup of sludge and grime, making your engine run smoother. It reduces stress on the starting system components to lengthen the life of your engine. This also means you can go a little longer between oil changes.


Many motor oils come in gallons, making it easier to measure when changing the oil yourself. However, Mobil’s formula is shipped out in quart containers. So, you’ll want to pay attention when changing the oil and measure it in quarts instead of gallons.

Honorable Mention
<strong>Motul 8100 X-cess Engine Oil</strong>

Motul’s X-cess engine oil is famous for being tested by endurance racers in the most rigorous possible conditions. Its synthetic formula is approved by a wide range of automakers, but it works especially well in diesel engines on late-model vehicles.


But we weren’t thinking of famous races when we decided to put 8100 X-cess on our list. We were convinced by how well the formula minimizes oil consumption. When going to change it after 5,000 miles, drivers often drain out the same amount they put in. This diesel oil is low-wear, extraordinarily efficient, and still makes a single change cost less than you’d pay at Valvoline.


It’s not perfect, however. The container nozzle is poorly designed. It’s hard to pull out, and sometimes sprays the oil all over the place when you get it loose. It also loses a few points for not being a 100 percent synthetic product, as there are a few crude additives.

Honorable Mention
Driven Racing Oil Semi-Synthetic Engine Oil

If you want to reap the benefits of traditional and modern diesel oils, the Driven Racing Oil Semi-Synthetic Engine Oil is a solid option. Unlike some of the competition that focuses exclusively on artificial chemicals, this 15W-40 oil uses both natural and synthetic ingredients. It includes a highly effective metallocene polyalphaolefins (mPAO) tech, meant to add to the wear-resistant features of the formula. It comes in a one-gallon container, held in an opaque plastic bottle to extend its shelf life after opening. This formula is compatible with OEM performance specs, though it exceeds the demands of the American Petroleum Institute for its category.


However, if a warranty covers you, be sure that you can use semi-synthetic engine oil. While this product is effective, completely synthetic oil is more consistent on a molecular level, so be sure this is the right oil for you.

Honorable Mention
Valvoline Premium Blue Synthetic Oil

Valvoline Premium Blue Synthetic Oil is a fantastic choice for trucks hauling heavy loads or vehicles contending with many hills on the highway. Its claim to fame as engine oil is that it remains the only formula recommended by Cummins (an American powerhouse in the engine industry). The support is due in large part to the high level of resistance against oxidation. It can prevent excessive wear and tear on the vehicle components while easily stripping away deposits. It works with all types of heavy-duty engines, with the formula being acceptable for gasoline engines as well. Coming with a full gallon of contents, this diesel oil is both reasonably priced and highly effective.

Honorable Mention
Quicksilver Marine Lubricant Diesel Engine Oil

For boats, the Quicksilver Marine Lubricant Diesel Engine Oil stands out from the crowd. Meant for use in turbocharged, direct injection diesel engines, this oil meets international standards for use on the water. It lubricates the engine’s internal components reliably, improving efficiency even in the toughest environments. Coming with over a gallon and a half of fluid, it reseals well in the opaque container. The spout makes pouring easy, limiting the risk of spills. When the engine’s in motion, this oil facilitates smooth movement, limits oxidation, and resists damage from overheating. Reliable and versatile, this diesel oil is best on boats but will also work with trucks.

Honorable Mention
Chevron Delo 400 SDE Heavy-Duty Diesel Engine Oil

Moisture is a natural byproduct of combustion, so your vehicle always has to contend with the risk of corrosion and oxidation. If you live in a high-humidity area, your diesel engine is contending with even more water vapors. The Chevron Delo 400 SDE Heavy-Duty Diesel Engine Oil best showcases its value as an oxidation preventer. It is made entirely out of synthetic materials, working with turbocharged four, stroke diesel and gas engines. The 15W-40 viscosity is compatible with most rides, offering the benefit of deposit reduction (and prevention). It incorporates a variety of high-end detergents and additives. Together, on a molecular level, they emulsify and scrub away debris. The result is improved engine performance with added resilience to ambient humidity.


Although you can use this oil on older vehicles, it truly shines on newer rides meant to reduce emissions. It’s best suited to newer vehicles that drive in humid climates since this will result in the most benefits.

Honorable Mention
Liqui Moly Synthetic Motor Oil

Liqui Moly’s German-made synthetic oil works in gas and diesel engines. It’s targeted toward modern multi-valve engine arrangements, and gets particularly good results on cold starts. The reason it made this list, though, is how well it holds up over long intervals between changes.


Leaving it in past the usual recommendation results in little loss of oil or fuel efficiency. Not only is Liqui Moly great at keeping your miles per gallon stable, it also hardly loses clarity by the 5,000-mile mark. At that time, you’ll also still be enjoying smooth starts and quiet idling.


Our complaints are few. Liqui Moly doesn’t work as well in turbocharged engines, and doesn’t generally maintain its standards of performance at high temperatures. It also comes at premium prices that might be too high for those who don’t change their own oil.

Tips

  • It’s important to carefully read the label of motor oil containers. They list essential information about the oil’s viscosity rating, application, and, sometimes, the additives it contains.
  • If you aren’t one to take your car to a mechanic, you can change the oil yourself, though it can be a bit messy. Ensure you don’t overfill your engine’s crankcase with oil. Overfilled oil can rinse into the crankcase and cause air bubbles to mix into the oil. This can stress the engine components, cause overheating, and even foul the spark plugs.
  • For anyone planning to use their vehicle to tow heavy loads, consider adding an oil cooler to your ride; that is if it doesn’t already have one. Oil coolers function similarly to your radiator and can dramatically increase the lifespan of your engine.
  • Before buying motor oil, read your vehicle owner’s manual to get more information about the car’s engine and what oil is best.
  • Getting your oil changed regularly is highly recommended. It will better protect your vehicle and engine from being damaged and save you money in the long run. The SAE advises using the same brand and viscosity as the vehicle’s manual recommends.

FAQs

Q: What is diesel oil called?

Technically, diesel fuel refers to the distilled petrol fuel oil used in a compression ignition engine system. The namesake ‘diesel’ is a shout-out to the German inventor, Rudolf Diesel. Don’t mistake fuel for oil, though: fuel is used for combustion while oil is meant for lubrication. The two work together to keep your diesel ride running smoothly.

Q: Which oil is best for diesel engines?

The go-to oil depends on the type of vehicle. 5W40 oil is preferred for cars, while 15W40 is better for larger rigs. The W stands for winter, where the number to the left indicates the viscosity rating at zero degrees Fahrenheit. The number to the right indicates the viscosity at temperatures up to 100 degrees Fahrenheit. The best oil, therefore, depends on your environment and the vehicle.

Q: What's the difference between diesel oil and regular oil?

The main difference between diesel and regular oil is the extra wear-resistant contents. Called zinc dialkyldithiophosphate, it works specifically to protect the catalytic converter of a diesel system to create proper combustion. Another thing to note is that diesel oil will almost always be thinner than regular oil—the high viscosity lets it move smoothly at a range of humidities and temperatures.

Q: Why is diesel oil so black?

When you pour it in, the oil should not yet have this dark hue. Instead, its color comes as a result of soot, something diesel engines generate in spades. It comes into the oil pan via the combustion chamber. Taking very little of this debris can change the color, so don’t be shocked if your used diesel oil looks like ink.

Q: What does the label on a motor oil container mean?

The API donut lets you know if the oil meets the current SL service rating as determined by laboratory and engine tests. There is also the SAE (Society of Automotive Engineers) star logo with the viscosity number and information on whether the oil has passed the energy-conserving test.

Q: How often should I change the oil in my vehicle?

Check your owner's manual to find out the maintenance schedule. Most vehicles can go between 5,000 to 10,000 miles before needing an oil change. However, if you do a lot of heavy towing, constantly stop-and-go, or go offroading frequently, you may need to change the oil more often.

Q: What is the shelf life of motor oil?

It mainly depends on how you store the motor oil. If it’s unopened and kept in a temperature-controlled environment, it should last several years. However, if the oil is left in an open container in a garage that experiences drastic shifts in temperature, it won't last as long.

Final Thoughts

Your ride deserves the best diesel oil to help it function better and last longer. The Royal Purple 15W-40 Oil is a worthy pick overall, improving fuel efficiency and preventing corrosion. Looking for a more budget-friendly choice? The Shell Rotella T6 Synthetic Diesel Motor Oil 5W-40 CJ-4 is an excellent way to preserve the health of your engine and your wallet.