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

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.

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.

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.

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.

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.

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. 

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 owner's 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.