Differences Between CK4 and CJ4: Which One Should You be Using?

Setting the standards for engine oil is one of many responsibilities of the American Petroleum Institute (API). As engine technology advances, API takes those developments into consideration, along with the most recent government regulations. Periodically, they create new criteria.

After about a decade of endorsing CJ4 as the benchmark lubricant for diesel engines, API published new service categories. That was in 2016, so fleets and shops have had a few years to start using the new oils. However, those with older trucks may not have made the switch yet.

If you’ve been putting it off, or wondering what the difference is between CK4 vs. CJ4, here’s the scoop:

The Newest Standards for Diesel Engine Oil

With truck manufacturers striving to build tougher, more fuel-efficient engines that put out fewer emissions than ever, updated service categories for diesel oil were needed. Newer semi engines are built to operate continuously and at greater internal temperatures than older trucks. Engines are smaller, too, and built with variable valve timing and advanced start/stop technology and combustion design.

In the new standards, there are actually two new categories for heavy-duty engine oils: CK4 and FA4. Both oil classifications are similar, but they vary enough that you’ll want to know the difference. Later on, we’ll also take a look at the comparison between CK4 and CJ4.

First, FA4 oils are more specialized. They are designed for engines built in and after 2017. The API description states that FA4 refers to XW-30 oils meant for “select” diesel engines that comply with 2017 standards governing on-highway greenhouse gas emissions. The oils must be appropriate for use on the highway, with up to 15 ppm sulfur content in the diesel fuel.

The CK4 description is a little broader. Also for use in four-stroke cycle high-speed diesel engines, these oils meet the 2017 non-road Tier 4 exhaust emission standards. However, this oil category replaces CJ4 lube technology. The formulation makes CK4 useful with sulfur content in diesel fuel up to 500ppm. The API notes, though, that using this category of oil with fuel that has more than 15 ppm sulfur could affect the oil drain frequency as well as the exhaust after-treatment system durability.

That’s not necessarily a bad thing, provided you don’t mix oil types.

Is CK4 Chemistry Better Than CJ4?

Good question—and one that hasn’t been explained in detail by professionals or lubricant manufacturers. We’ll discuss the benefits of CK4 vs. CJ4 in a moment, but if you’re curious about the chemistry, the closest thing you’ll get to an answer is comparing labels on various heavy-duty engine oils. You’ll find that CK4 oils tend to have higher total base numbers (TBNs). They are also higher in calcium, zinc, boron, and phosphorus. Plus, they tend to be lower in SAPS. But considering those levels in CJ4 oils are fairly low anyway, lower additive content isn’t a huge issue.

Comparing CK4 vs. CJ4

The new oils provide better oxidative stability, more aeration resistance, and enhanced shear stability. In fact, in order to meet the CK4 oil API standards, lubricants must prove themselves in two new tests: the CAT Aeration test and the Mack T13 test.

Additionally, CK4 oils provide better protection for engines than CJ4 oils. Using CK4 should increase the time between oil changes and improve fuel economy thanks to lower viscosity grades.
You find familiar, common grades such as:

• 5W-30
• 5W-40
• 10W-30
• 15W-40

All Diesel Oil Brands Aren’t the Same

Just because API sets a standard that doesn’t mean that all oil brands are the same across the board. Some see the standard as a minimum to meet. Others see it as a starting point for creating a better product.

When it’s a question of what brand to use in the equipment that runs your business, it makes sense to go one that exceeds the standards. If you have a trusted brand, there’s no reason not to consider continuing to use it. However, when you’re looking at CK4 vs. CJ4 and making the switch, it might be a good time to consider other oils with good reputations that you haven’t used before.

If you decide to shop brands, become a label reader. Try to find out if the brand has done its own testing in addition to the API-required trials. Word of mouth is invaluable, too—ask heavy-duty techs what they use and why they recommend it.

Backward Compatibility

Have you put off switching to a new oil because you aren’t sure whether it will work in your pre-2017 engine? The good news is that CK4 is backward compatible. That means even though it was created for new engines, it’s fine to use in older trucks, too. In fact, the newer oil makes your older model semi run better—CK4 is supposed to improve engine performance and increase fuel economy.

Keep in mind, though, that FA4 is not backward compatible. That is another difference between the two new oil classes. FA4 is specifically for newer heavy-duty engines. There may be exceptions, though. Those with older model trucks who are interested in using FA4 should consult their OEMs to find out if FA4 has been tested in their specific engine and if it was found to work well.

Consequences for Not Using CK4

With the benefits of CK4 vs. CJ4 in mind, it’s easy to see why you should use it. For older trucks, it’s not mandatory or even necessary. But if it will improve your semi’s fuel efficiency, overall performance, and lifespan, changing to CK4 is a practical move.

What about the reverse, though? Having been formulated in the past to maintain older technology, CJ4 oil isn’t exactly forward compatible. However, even though it isn’t likely to optimize Tier 4 performance, it won’t damage a newer engine.

Still, there can be negative effects if you use an older formula oil such as CH4 or CI4 in a newer engine. Those oils could:

• Pollute the catalytic matter in the after-treatment system, preventing it from working properly
• Cut the engine life short by plugging the diesel particulate filter
• Hinder performance and efficiency

The Issue With Accidental Top-Offs

Fleets with a combination of older and newer semis could run into the problem of accidentally topping off an engine with the wrong oil. A mishap like that can be avoided through your PM tracking program; just schedule the maintenance for newer and older models on different days. That way, when techs reach for the oil to top off a low level, the wrong formulation won’t even be among the ready supplies.

What if an accidental top-off occurs? The good news is that a one-time slip-up shouldn’t cause harm or breakdowns, especially if you use less than a gallon. CK4 is compatible with CJ4, and they will mix together—you probably won’t even notice a difference in how the truck operates.

However, to gain the full benefits of CK4, you should drain the CJ4 from your engine and entirely replace it with the newer oil. Keep in mind, too, that problems can arise if you top off CJ4 with FA4, or perform a complete oil change in an older truck from CJ4 to FA4 without checking with the OEM first.

CK4 vs. CJ4: Making the Switch

Naturally, when you add a truck with a Tier 4 engine to your fleet, you should plan on using the newest oil formulation. If you have a combined fleet or are working exclusively with older heavy-duty engines, it’s a good idea to consider switching over—just check with the manufacturer before making a change like that.

When making the switch, you’ll continue to use the same viscosity grade. As we mentioned above, your best bet is to make the switch during a complete oil change. That way, your truck or trucks will reap the optimal benefits of the better lubricant.

We’ve talked a lot about fleets and truck owners using CK4 vs. CJ4, but shops should be using the newer oil by now, too. There will be customers who still use the older formulation, but you’ll probably see a gradual shift to the newer oil over time. For now, that means stocking both types of lubricant and making sure your mobile service techs carry both on their trucks, as well.

Your Insurance Policy for Using the Right Oil

Whether you manage a fleet, have just started a repair shop, or have been in the repair business for years, Fullbay can help make sure you use the right type of oil every time. It keeps a history of all the PMs performed on each vehicle, and that includes what type of oil was used in the last change—helping you avoid accidental top-offs. Plus, you’ll be able to see at a glance which trucks are using CK4 and which ones still need to change over from CJ4.

If an older truck shouldn’t make the switch and needs to stay on the older formulation, you can even make note of that in Fullbay. What’s more, the inventory feature will ensure you always have a supply of both oils when you need it—and the Fullbay Marketplace makes it easy to stock up on more.

Fullbay is a user-friendly program that’s accessible on practically any device that makes heavy- duty repair and maintenance a snap, but it does so much more than just track PMs. Fill in the form below to get a taste of what Fullbay can do for your fleet or shop.