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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Making sure your vehicle’s engine is running at its best should always be a top priority. To help boost the performance of your vehicle, finding the best motor oil will keep it running smoothly for years. If you have a diesel engine and haul heavy loads, you’ll need a good diesel oil most of all. Here’s our list of the best heavy-duty diesel engine oils to keep your vehicle in peak condition.

  • Best Overall
    Royal Purple 15W-40 Oil
    This superior diesel motor oil doubles as an excellent choice for gasoline engines as well. It’s made up of premium-based oils with additive technologies to help give your engine a high-quality boost in performance.
    The compound within the bottle prevents metal-to-metal contact and keeps rust from building up in the engine compartment. The materials clean the engine, flushing out sludge and gunk.
    The container may not come with the correct amount of fluid. For instance, a gallon bottle may contain a few fewer ounces than advertised. New car owners must drive the vehicle at least 8,000 miles before adding this oil.
  • Best Value
    Shell Rotella T6 Synthetic Diesel Motor Oil 5W-40 CJ-4
    This heavy-duty synthetic blend of diesel oil protects and cleans the engine to give you a more comfortable ride. The improved wear performance provides a significantly increased level of protection against harmful engine wear.
    Shell’s Triple Protection Plus technology allows it to work great in cold or warm environments. It protects against soot, dirt, and other debris from building up and blocking the flow of oil to your engine, giving your engine a quicker reaction time when starting.
    The bottle could spring a leak during shipping, so be wary when opening the packaging.
  • Honorable Mention
    Mobil 1 Synthetic Motor Oil 0W-40
    Mobil 1’s oil protects, lubricates, and boosts a vehicle's performance capabilities on the road. The compound fights to prevent leaks and keeps critical engine parts in peak condition.
    The advanced, fully synthetic formula prolongs the life of your car’s engine and blocks the buildup of sludge and grime. It reduces stress on the starting system to lengthen the life of the engine.
    It only comes in quart containers, so you’ll want to be careful when it comes to measuring the amount you need.

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

Full Synthetic

Full synthetic diesel motor oil is made up of a complex and unique molecular structure. It is infused with additives to deliver optimal wear protection and performance for your vehicle’s engine. Unlike regular oil, it is not derived from whole crude oil, so it’s formulated without any of the impurities that you’d find in conventional oil. The best synthetic diesel oil brands use a proprietary blend of anti-wear and cleaning additives to make your motor run at its best.

Synthetic Blend

Synthetic blend diesel motor oil is a mix of conventional oil and a brand’s synthetic base oil. It’s a blend of conventional oil combined with synthetic compounds to better protect the vehicle’s engine and performance capabilities. 

Top Brands 

Mobil 1

Introduced in 1974, Mobil 1 offers synthetic motor oil and lubricant products. Its synthetic motor oil is perhaps the most recognized brand in the business, with prestigious auto manufacturers such as Porsche and Mercedes-Benz using Mobil 1 synthetic oil in all their vehicles. One of its best-selling products is the Mobil 1 Synthetic Motor Oil 0W-40


Castrol's headquarters are in the United Kingdom, and the company, which was founded in 1899, operates in over 40 countries. It produces lubricants for motorcycles, two-stroke and four-stroke engines, and gas and diesel engines. One recommended product is Castro’s 03084 Edge 5W-30 Advanced Full Synthetic Motor Oil.

Liqui Moly

Founded in 1957, Liqui Moly is a German company that manufactures oils, lubricants, and additives. The brand prides itself on offering premium quality products at a more accessible price point than its competitors. One of its top products is the Liqui Moly 2041 Premium 5W-40 Synthetic Motor Oil.

Royal Purple

Established in 1986, Royal Purple is an American manufacturer of lubricant products for automotive, industrial, marine, motorcycle, and racing usage. It is best known for its motor oil products and garners the endorsement of car enthusiasts for its high-performance formula. One popular product is the Royal Purple 15W-40 Oil.


Valvoline Inc. was founded in 1866 and is one of the world's top producers of premium lubricants and automotive services. Its headquarters are in Lexington, Kentucky. One of its most popular motor oils is the Valvoline 5W-40 Premium Blue Extreme Synthetic Diesel Engine Oil.

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.
  • Over $20: 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


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.

Other Considerations

  • Compatibility with Existing Oil: Before you add diesel engine oil to your vehicle, it’s important to note if the brand is compatible with other types of oil. If it isn’t, you’ll have to drain the existing oil before filling it up with the new oil. It’s important to consult your owner’s manual to verify which type of oil works best for your vehicle.
  • Type of Driving: Finding the right diesel engine oil also depends on what kind of driving you’re doing. Vehicles with a diesel engine frequently tow or carry heavy loads or undergo more stress than an average car.

Best Diesel Oil Reviews & Recommendations 2019

Best Diesel Oil Overall: Royal Purple 15W-40 Oil

Royal Purple 15W-40 Oil

One of the greatest things about this diesel motor oil is its versatility. While not only being an excellent choice for diesel-engine cars, it also works best on gasoline engines. Plus, it can be used with synthetic and conventional motor oils. Royal Purple combines “premium base oils with additive technologies” to create high-quality motor oils, and this one sure doesn’t disappoint.

Those enhanced additives help prevent metal-to-metal contact and keeps rust from building up in the engine compartment. A great benefit we found is this diesel engine oil works on older model vehicles as well. So, if you need to start up one of your old pickup trucks, this will get the engine purring. The compounds making up this oil help to clean and flush out sludge and gunk buildup. It even works on high mileage vehicles.

While being one of the best diesel oils we recommend, you may not get an entire gallon when purchasing. The container may run a few ounces shorter than advertised, so you may need to buy multiple containers or measure to make sure it’s near one gallon or more. For anyone with a brand new vehicle, it’s recommended to wait until you’ve driven 8,000 to 10,000 miles before using this motor oil.

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

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.

At a far less price than other brands of diesel oil, this one holds up to some of the best. However, be warned when unpackaging the container, there have been reports of consumers receiving bottles that have leaked. Also, it does come with a money back refund, but many consumers say they’ve had issues getting their return.

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Best Diesel Oil Honorable Mention: Mobil 1 Synthetic Motor Oil 0W-40

Mobil 1 Synthetic Motor Oil 0W-40

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, full 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.

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  • 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 does the label on a motor oil container mean?

A: 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?

A: 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?

A: 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

For anyone who needs a good diesel motor oil to help boost their engine’s performance and fuel efficiency, we recommend the Royal Purple 15W-40 Oil.

If you want to save some cash and still invest in one of the best diesel oil’s on the market, go for the Shell Rotella T6 Synthetic Diesel Motor Oil 5W-40 CJ-4.

Leave us some thoughts and comments on our picks below.