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The 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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BYCorrina Murdoch/ LAST UPDATED ON September 28, 2021

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.

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

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We can’t put our own hands on every item available. In these instances, we put our collective experience in journalism, research, and prior product testing to use to make our product picks. Items that are used by our own staff may get earnest endorsements as well, but we’ll never accept fees or bonuses to sell you stuff we’re not actually excited about. Affiliate revenue is always disclosed.

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Our reviews are driven by a combination of hands-on testing, expert input, “wisdom of the crowd” assessments from actual buyers, and our own expertise. We always aim to offer genuine, accurate guides to help you find the best picks.

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Best Diesel Oil Reviews & Recommendations 2022

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.

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.

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.

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.

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.

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.

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.

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.

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.

Our Verdict

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.

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.

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.

FAQs

You've got questions. The Drive has answers.

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: 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.

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