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The Best Oils for 6.7 Cummins: Keep Your Engine Running Smoothly

Keep your engine running at peak efficiency with our picks for the best oil for Cummins engines.

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BY Corrina Murdoch / LAST UPDATED ON May 28, 2021

If you drive a Dodge RAM, whether it’s a 2500 or a 3500 pickup, you know the thrill of the sheer power it supplies. These engines have a proud history dating back to 1919, when Rudolf Diesel partnered with William Cummins — that’s right, the inventor of diesel and founder of Cummins motors have intertwined stories. Literally first to market, this Indiana-based company took the industry by storm. It also offered the brand a leg-up on innovation, enabling them to advance the technology, refine the parts, and craft fluids meant to truly optimize their engines. Cummins are prevalent in Dodges, with the 6.7 boasting up to 400 horsepower and impressive torque. Of course, to access this ability, the engine relies on maintenance and lubrication. Finding the best oil for 6.7 Cummins engines is about more than optimizing efficiency, it’s about keeping your ride healthy for longer, too. To lend a hand, we’ve hunted down the best oil for 6.7 Cummins rides to keep your vehicle in fighting form.

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Benefits of Oil for 6.7 Cummins

  • Keeps your engine healthy. Your 6.7 Cummins needs oil to keep things running smoothly — literally and figuratively. It creates a hydrophobic barrier that keeps moisture out, prevents buildup, and moves parts without friction grinding them down. Picking the best oil depends on the vehicle and its age, but by choosing the right one, you can keep your engine working far longer.  
  • Limits the frequency of top-ups. A 6.7 Cummins engine is a powerhouse with impressive horsepower and torque. It also means your oil undergoes a lot more strain than it would with a weaker system. Cummins requires a fair bit of oil, though older models tend to consume it in excess (often due to flawed seals). Picking the best oil for your 6.7 Cummins can slow the process, meaning you need to top it up less frequently. 
  • Better for the environment. A leaky oil system or compromised combustion do nothing but harm the ecosystem (not to mention your truck). By properly maintaining the oil system with a well-chosen product, you are able to create cleaner emissions. Many modern diesels are outfitted with cleaner output systems, and picking a good oil definitely helps the cause. 
  • Recommended by manufacturer. If the company that crafted the engine tells you to use a certain kind of oil, keep it at a specific level, and change it at a set frequency, there is probably a good reason. Using a compatible oil and taking care to keep your levels where they should be by checking the dipstick after a long drive goes a long way to vehicle longevity.
  • Improved fuel economy. When you get a cleaner burn, resulting from a properly oil-treated engine, your combustion results are better. A combustion engine takes fuel and oxygen, adds the catalyst (by way of heat or spark), and burns the fuel. The result is carbon dioxide and water. However, imperfect burns can cause other molecules. Oil prevents overburning, the risk of carbon monoxide output, and stops soot from building up. 
  • Prevents corrosion. By standardized definitions in the industry, set forth by ASTM D-975, you can expect around a five percent water content in your fuel. Water wreaks havoc on internal engine components causing oxidation, corrosion, and untimely wear. Oil puts up a hydrophobic barrier (latin for water-fearing). This prevents water from doing damage and keeps things running properly. 
  • Protects the seals. Older vehicles are prone to damage, just because the system has gone through a lot of wear and tear. Even with routine oil changes, as the odometer ticks forward, the need for oil increases. Seals dry out and can lead to leaks. Choosing the right oil not only prevents this, but it can also fix the problem after the fact.

Types of Oil for 6.7 Cummins

Synthetic Oil

One of the most modern 6.7 Cummins diesel systems, the turbo 2021 has an impressive compression ratio of 16:2:1 when in high output. This means the engine undergoes combustion at high heats and high pressures. Synthetic oil is a preference for handling these conditions, since it is able to withstand that extra strain on a molecular level. Yes, it comes at a higher cost because all the materials are artificial. However, you can get these oils at various viscosities and with different treatments, customizing the selection to your pick. The key takeaway: Synthetic oil is tops for vehicles under strain like pickup trucks.

High-Mileage Engine Oil

In the vast majority of cases, high-mileage engine oil is a subtype of synthetic diesel oil that is meant for vehicles with over 75,000 miles on the odometer. In theory, you can get upwards of 300,000 miles out of these engines, but once the mileage stacks up, switching oil is advisable. High-mileage oil is designed with the standard base oils, though includes additives like conditioning agents and oxidation preventatives. It softens seals, restoring them to proper function (provided the damage isn’t too extensive). The key takeaway: High-mileage engine oil is meant for older 6.7 Cummins engines. 

High-Viscosity Motor Oil

Viscosity matters. If the oil is too thin, then it won’t effectively complete its task. If the oil is too thick, it can’t move throughout the system. Since this factor directly impacts the oil’s ability to lubricate, finding the right viscosity is essential. High-viscosity oil lubricates more evenly, simply because it’s slippery and can coat the parts quicker. The SAE J300 viscosity chart details the specific metrics, so you can interpret coded viscosity notes like 15W40. The number to the left is how it handles cold. The number on the right is how it handles heat. Use the viscosity breakdowns, consider your environment, and pick accordingly. The key takeaway: When in doubt, choose high-viscosity oil.

Detergent Oil 

A popular type of oil, while all oil for 6.7 Cummins engines are made out of a set of base oils, the additives used to enhance performance vary. Though you can find some oils entirely free of detergents, these useful chemicals are effective at scrubbing out imperfections in the oil. Addressing deposits while also performing all the essential tasks of a motor oil, because of the chemical nature of magnesium sulfonates (the most common detergent), it retains structural integrity under pressure and heat. Plus, you don’t have to change the oil as frequently if you use a detergent option. The key takeaway: Detergent oils are a vast improvement on non-detergent motor oils. 

Conventional Oil 

Taking raw crude oil and refining it into a workable motor oil for your ride, conventional oil is the traditional approach to running your engine. It dates back to when Castrol first used mineral-based castor oil as an ingredient. Now, while you can find it on the market, it is definitely less common. This is largely due to the higher ratio of imperfections. It’s cheaper, but both in terms of quality and price. The imperfections may not result in issues right away, but using this type of oil can lead to issues. The key takeaway: Natural is great in theory, but synthetic oil takes the cake for 6.7 Cummins engines. 

Top Brands

Valvoline

Established in 1866, Valvoline is almost as old as cars themselves. Originating through research into crude oil by Dr. John Ellis, what was intended as a medical discovery led to the creation of lubrication for trains. Taking off from there, Valvoline reached trademarked status in 1873. All uphill from there, it expanded research and development to create many industry firsts. The first was an oil with almost 20 additives, removing the need to apply them one by one. It’s next big development was an all-weather racing oil. Since then, it’s continued to grow, now traded on the New York Stock Exchange under the ticker name VVV. It supplies vehicular fluids to 140 countries, including the Valvoline High Mileage 10W-30 Synthetic Blend, a solid pick for 6.7 Cummins. 

Cummins

The tales of diesel and Cummins are intertwined, solidified through a business partnership between William Cummins and Rudolf Diesel. Though the company changed hands many times since, it took a turn for greatness when Irwin Miller took over operations, turning it into an international powerhouse. The company turned a profit in only three years, segueing Cummins into becoming the industry’s first provider of a 100,000-mile warranty. Its engines and fluids remain as relevant today as they were 100 years ago, highlighted by the continued popularity of the Dodge RAM 6.7 Cummins engine. To care for it, this brand supplies Cummins Onan 15W40 Oil for smooth operations and improved longevity. 

Best Oil for 6.7 Cummins Pricing

  • $17 to $35. In this category, you can get up to 5 quarts of oil. It can be a full synthetic or synthetic blend. Some of the products come in one-gallon containers, others in 5-quart or 2.5-gallon containers. Viscosity ranges are 5W-20 to 15W-40.
  • $35 to $80. This category features a similar viscosity as the lower price range but you can get as many as three 1-gallon containers for your money. Only full synthetic oils are found in this price range.
  • $80 and up. This range offers 5-gallon pails of synthetic motor oil for your Cummins 6.7 engine. Viscosity ranges are from 5W-40 to 15W-40. This price category includes one oil that is specially blended for Ford under the Motorcraft name. 

Key Features

Lubricating Power

Obviously, you want the oil you choose to do its main job: lubricate the components of your Cummins 6.7 diesel engine. The OEM recommendations can guide you here, but you may want to read what others are saying about the oil you are considering with regards to its lubricating power. If the oil does not do this main job correctly, efficiently, and for a good price, it’s not the oil for your truck.

Weather Considerations

You want your oil to protect your engine in extremely cold and extremely hot weather. It can’t thicken too much in the winter or thin out in the summer, or it could inhibit proper starting and operation. Dust and dirt conditions are also a consideration. If you work in dusty, dirty areas, or drive off-road, your oil needs extra detergent power, and your engine will need more frequent oil changes as well. 

Environmental Impact

Many drivers are concerned with how their vehicle affects the environment, especially air pollution. Some diesel oil producers specially formulate some of their products to help reduce soot and nitrous oxide emissions. Others formulate their oil so it works best in the newer emissions-treatment engine designs. 

Other Considerations

  • Price. If one brand of oil for 6.7 Cummins is value-priced and does the same (or better) job of lubricating your engine as a higher-priced brand, why waste your money? Shop and compare. It could very well save you a lot of money, especially over the long run. Also, watch for sale prices and quantity deals.
  • Quantity. You have your choice here. You can purchase a 1-quart size, 2.5-gallon size, 1-gallon size, or a 5-gallon bucket. Some of the quart sizes only come in 5- or 6-quart cartons. Similarly, some of the gallon sizes come in 3-gallon cartons. Naturally, you’ll want to determine how much you need but also if you buy in quantity, whether it saves you money. 
  • Brand Reputation. It’s wise to buy from a brand you know and trust. You don’t want to go with a questionable brand when choosing something as important as the oil that is responsible for keeping your Dodge Ram truck operating as it should for a long time. Well-established national brands have a good reputation for a reason.  

Best Oils for 6.7 Cummins Reviews & Recommendations 2021

Best Overall
Quaker State 10W40 Protective Oil

Finding an oil for your 6.7 Cummins is all about something able to withstand demanding conditions. The Quaker State 10W40 Protective Oil exceeds these demands, coming complete with powerful additives to address wear. It is geared towards rides with over 75,000 miles on the odometer. Higher-mileage Cummins engines tend to become oil-guzzlers, requiring top-ups more frequently than younger counterparts. It could be due to the added demand on the engine or as a result of leaks from cracked seals. To address this, the Quaker State oil is complete with conditioning additives that treat seals and put a halt to leaks. It keeps your selas working while also incorporating some extra additives to reduce adjustment friction and slow oil consumption. Powerful and reliable, this diesel oil can help extend your engine’s lifespan while also enhancing its function. 


One criticism about this oil is in the packaging. It comes with over a gallon of contents, yet the handle has no grip accommodations and the spout is too broad. Be sure to use a funnel when dealing with this oil to prevent spills.

 

Best Value
Cummins Onan 15W40 Oil

Vehicle costs add up, from fuel to transmission fluid to oil. To shave a few dollars off this regular expense, the Cummins Onan 15W40 Oil is a worthy candidate. For starters, it has a universal compatibility rating, meaning you don’t have to worry about interactions with your existing oil. Despite being so reasonably priced, it doesn’t skimp in terms of quality. This oil is designed to work specifically with Cummins systems, meaning it is able to efficiently limit oil consumption. It is particularly useful at warm temperatures, where viscosity is prone to rapid increase. The friction regulators included as additives prevent this from compromising lubrication. By also addressing oxidation damage, this oil is able to help your engine perform more reliably. Ideal for anyone working on a budget, this is a worthy value pick. 


Bear in mind, though, that while the oil comes at a great price, it comes in a small quantity. For top-up use, it’s great. For an oil change, you’re going to need much more oil to get the job done.

Honorable Mention
Mobil 1 Turbo Diesel Truck Oil

If you live in an area more prone to snowstorms than heat waves, the Mobil 1 Turbo Diesel Truck Oil is a solid candidate. It stands out from the other candidates through its modern technology, including advanced additives to protect your vehicle well. It is meant specifically for vehicles handling the impressive horsepower supported by a 6.7 Cummins. By reducing the oil loss and improving fuel economy, it helps your whole ride function better. Meant to be compatible with any type of oil on the market, it is particularly useful with modern vehicles. If your ride is equipped with Exhaust Gas Recirculation, meant to limit emissions, this oil is particularly useful. Since these eco-friendly features impact the heat in the system, as well as oxidation effects, it is important to find an oil that can keep up with the demand. Mobil 1 is formulated to handle adversity, making it deserving of a shoutout on this list. 


Of course, nothing is perfect. This oil is a 5W40 after all, and the smaller the number to the left of that W, the more it is geared towards cold weather. Be sure to keep your climate in mind when making your pick. If contending with heat, look for something designed with the proper viscosity for hot situations.

Best for Turbos
Shell Rotella T6 Synthetic Diesel Engine Oil

Shell Rotella T6 is a state-of-the-art, fully synthetic motor oil blend that’s formulated to improve fuel economy up to 1.5 times its usual level. Its Triple Protection Plus technology might sound made up, but it’s actually a trustworthy mixture of additives that works to keep a Cummins engine safe from deposits.


What really got Shell Rotella T6 on our list is its performance in turbocharged engines. If you’re a turbocharger enthusiast who’s afraid that a 5W-40 oil will never hold the viscosity that you need to maintain pressure in a powerful engine, worry no more. This lube outperforms a lot of zero-weight manual-recommended oils.


Beware if you buy: Shell has a nasty habit of failing to fill the bottles all the way. It’s a great-quality oil, but you might have to buy 2 gallons just to ensure you have one. This can result in shipping issues, since the air gap leaves the plastic more vulnerable to impact. That said, it’s a good-quality oil, and the risk of damage is limited, keeping this synthetic oil on the honorable mention list.

Honorable Mention
Valvoline High Mileage 10W-30 Synthetic Blend

Given the number of times Valvoline has showed up on this list, you shouldn’t be surprised to see the brand again. This time, we’re featuring its high-mileage solution, which is available in a wide range of sizes and viscosities.


In Cummins engines with more than 75,000 miles on the odometer, Valvoline high-mileage oil cleans out sludge and prevents new deposits from forming. It includes the extra detergents and protections older engines need to reverse wear. The seal treatment performs especially well—we’ve seen it stop leaks altogether and keep powerful engines running quietly at more than 200,000 miles. It also comes at a great price.


What’s the catch? This is a synthetic blend, not fully synthetic or Dexos-certified, so it might not be the right choice for aging GM vehicles. Don’t believe any seller who tells you it’s Dexos. Also, like many motor oils sold online, there’s a risk of the caps leaking.

Honorable Mention
Mobil 1 High Mileage Full Synthetic Motor Oil

Mobil 1 is the official oil of NASCAR, but even if you aren’t regularly driving stock cars at 200 miles per hour, you can get great performance using this lubricant. Like many of our favorites, it contains a seal conditioner that can prevent engine leaks, and reverse leaks that have already started.


As a high mileage synthetic oil, its additives are designed to prolong engine life, but it’s also ideal for extended use: You can go 15,000 miles on this before protection and viscosity really begin to break down. It also flows especially well on cold mornings, so if you’ve been suffering from sluggish starts in the winter, this might be the cure.


One thing that makes us less enthusiastic about Mobil 1 is that, despite claiming to be a high mileage oil, it actually loses a bit of power with engines over 75,000 miles. It’s excellent at stopping leaks but doesn’t last a year at that age, and only quiets engine knocking rather than silencing it all together. In our opinion, it’s also overpriced for 5 quarts.

Honorable Mention
Shell Rotella T5 Synthetic Blend Diesel Engine Oil

This engine oil is similar to the Shell Rotella T6 we spotlighted above, with a few key differences. While Rotella T6 is completely synthetic, T5 is a synthetic blend that includes some crude products. That’s not a knock against it, though: It’s a low-ash, low-emission motor oil that’s perfectly suited for use in modern engines.


If we had to describe Rotella T5 in one word, it would be “flexible.” We don’t often see oils with the versatility to work in a Cummins 6.7, motorcycle, ATV, lawnmower, and chainsaw. It promises increased fuel economy and wear protection, and delivers on both counts. We especially like how well it maintains pressure in turbocharged engines.


One issue is that, while it’s a good oil, the cap leaves something to be desired. The threading can chip, making it almost impossible to get the seal back. Since it comes with a whole gallon, you’ll probably need to store it. Be careful when opening and retightening it, and you should be fine. 

Honorable Mention
Delo 400 XLE Synthetic Blend Oil

The last entry in our list of favorite engine oils for a Cummins 6.7 is this synthetic blend from Chevron. Delo 400 XLE is formulated to clean out deposits, protect turbocharged engines, and maintain rigorous modern emissions standards. One gallon comes at an economical price, but that’s not all it offers.


Delo 400 XLE performs well as a mixed-fleet oil. Get a case of it, and you can boost the fuel efficiency of gas and diesel engines on cars, trucks, boats, and outdoor equipment. We saw the best results at searing highway temperatures, where other oils break down under the strain. Despite not being explicitly a high mileage oil, it also works well above 200,000 miles.


The only drawbacks of going with this oil is that it’s not a full synthetic, which might not grant the protection recommended by your owners’ manual. The bottle is also poorly designed, with the handle on the same side as the spout, making it a bit hard for people with mobility issues to pour correctly.

Tips

  • Always check your owner’s manual for the recommended oil for Cummins 6.7 engines. If you don’t go with the recommended oils, make sure the oil you choose meets or exceeds certain American Petroleum Institute (API) and National Institute for Automotive Service Excellence (ASE) standards.
  • Oils are carefully formulated to operate in specific temperature ranges. Buy the proper weight for your environment and season. A lower first number is a thinner base oil for extremely cold temperatures. 
  • Be careful when changing your oil to not over or under fill your Cummins engine. Too much oil in the crankcase/oil pan can create excess pressure, which can push oil past seals and cause damage. 
  • When changing your oil, it’s is a great time to change the air and fuel filters as well. Clean air and fuel filters will help your engine run more efficiently and cleanly, giving you better mileage. 

FAQs

Q: What’s the difference between 5W40 and 15W40?

The number to the left of the W refers to the viscosity in cold situations. The number to the right references its thickness in hot settings. To achieve the properties of the 5W standing, the oil is synthetically made. Oil that is 15W40 may be synthetic or blended, though is more likely to include mineral grade components. If you’re dealing with cold-starting the Cummins, 5W40 is preferable. Dealing with a heatwave? Look for 15W40 for its high heat tolerance. 

Q: How much oil does my Cummins take?

It’s always best to follow the manufacturer recommendations. The specific amount of oil required will depend on the make and model. Many vehicles use a 6.7 Cummins, with most requiring 12 quarts for a complete oil change. For top-ups, it depends on your vehicle’s condition and the oil you’re using. Cummins are known for consuming a lot of oil, especially the older models. 

Q: How many miles does a 6.7 Cummins last?

Cummins was the first company to offer 100,000-mile warranties, so the brand stands behind its products. It’s reputed that you can get up to 350,000 miles out of the vehicle, but that requires pristine maintenance: regular oil and filter changes, responsible driving, and amenable road conditions. You can expect at least 100,000 miles, but after that threshold, it becomes more of a factor of wear and tear, climate, and driving habits. Take care of your Cummins and it will return the favor. 

Q: How often should you change oil in a 6.7 Cummins?

Follow the official maintenance schedule (especially if you’re on any kind of service contract). The frequency depends on your vehicle’s age, any existing damage, road conditions, and the type of oil. Because it also varies by the make and model of the vehicle, consult this chart to be sure. It’s best practice to change your oil every 15,000 miles; but, if your warranty says to do it sooner, stick to those parameters.

Q: What weight oil should be used in a 6.7 Cummins engine?

Cummins specifically recommends two Valvoline oils for its engines. The 15W-40 oil is for temperatures above 0 degrees Fahrenheit while the 5W-40 is for extremely cold temperatures. 

Q: Are synthetic oils better for 6.7 Cummins engines?

That’s open for debate. Some manufacturers and engine builders state that synthetics are better, while others prefer blends. What is universal is that the colder the environment, the lighter weight the oil needs to be to reduce wear during cold starts. 

Q: Is Valvoline Premium a good motor oil for 6.7 Cummins engines?

Valvoline Premium Blue and Premium Blue Extreme motor oils are specifically recommended by the Cummins factory. Cummins has tested these oils extensively and determined they have characteristics that make them ideal for diesel engines.

Final Thoughts

Now that you know the ins and outs of finding the best oil for 6.7 Cummins engines, you can make your pick. It could be the versatility and efficiency of our top pick, Quaker State 10W40 Protective Oil. If you’re looking to save money and preserve quality, you can go with the Cummins Onan 15W40 Oil, a clear value pick. Whatever mileage you have and terrain you face, there’s the right oil out there for your truck.