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.
The Drive and its partners may earn a commission if you purchase a product through one of our links. Read more.
BY Corrina 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.
Why Trust Us
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
- 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
- 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.
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.
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.