The 6 Most Common ISB 6.7 Cummins Engine Problems

Many also associate the Cummins name with some of the best light truck diesel engines ever. However, no engine is perfect and the 6.7 Cummins diesel is no exception. The 5.9 Cummins legendary reliably unfortunately didn’t translate as well to the redesigned new engine.

The new engine received numerous emissions systems that have ultimately been very problematic since the engines introduction. In this article, we discuss the most common problems on the Dodge Ram 6.7 Cummins engine as well as overall reliability.

6.7 Cummins Engine Problems

• Clogged DPF
• Turbo failure
• Heater grid bolt
• Head gasket failure
• Fuel dilution
• Cracked EGR cooler

Problems with the 6.7 Cummins often come down to emissions parts. However, the turbos and head gaskets are known to run into occasional failures too.

Generally speaking, the reliability rankings are as follow: 2013-2018 models, 2007.5-2012 models, and the 2019-2020 6.7 Cummins comes in last due to the CP4.2 exploding.

If you would rather consume this content via a video, check out our 6.7 Cummins Common Problems video below:

1) DPF Clogging

Diesel particulate filter (DPF) clogging is a common problem on the Dodge Ram 6.7 Cummins. Initially, Dodge opted to avoid using diesel exhaust fluid (DEF). Without DEF the B6.7 diesel must run a little bit on the richer side to reduce NOx emissions. This in turn leads to more particulates, also known as diesel soot, which can quickly clog the DPF.

These clogging issues were so problematic early on that Dodge rolled out multiple PCM re-flashes in an attempt to reduce the occurrence. In 2013, Ram pickup trucks receive SCR emissions control systems along with diesel exhaust fluid. This helps reduce particulates, so DPF clogging is less common on the later year 6.7 Cummins. However, it still affects many trucks – especially as mileage builds up.

It’s pretty bad for a turbodiesel engine to run with a highly clogged exhaust DPF. This causes a build-up of back-pressure for the 6.7 Cummins, which can lead to more heat and stress on the engine. As such, it’s important to ensure your 6.7 Cummins DPF is functioning properly. Some have success in washing out clogged diesel particulate filters. Others decide to delete the DPF completely.

Clogged DPF Symptoms

• Power loss
• Long crank
• Reduced power mode
• Engine fault codes

One of the main symptoms you may notice is power loss on the 6.7 Cummins with a clogged DPF. If exhaust gases can’t escape efficiently you’ll have a build up in pressure. That causes the 6.7 engine and turbo to run poorly. This is especially true if you end up in low power mode due to the 6.7 Cummins DPF clogging. You may also notice long cranks or an engine fault code.

DPF Replacement

The DPF is an expensive piece of emissions equipment. Even a refurbished 6.7 DPF can run north of $1,000 while original filters are nearly double that. Dodge and Ram 6.7 Cummins owners have a few options. Aftermarket higher performance diesel particulate filters exist, but those still often come in over $1,000. Some have success in pressure washing the OEM 6.7 DPF. Trying to clean the filter may not work at all, but if it does it’s likely to be a shorter-term solution.

Ultimately, this leads some to go the route of completely deleting the 6.7 Cummins DPF with an aftermarket exhaust. This is definitely the easiest on the budget and most effective long-term solution. However, DPF deletes do come with some legal concerns due to emissions.

2) Turbocharger Failure

Turbo problems or failures are more common on earlier model 6.7 Cummins engines. However, it can happen on any year as turbochargers naturally take a lot of abuse. We titled this section turbo failure, but there are a few issues that may not result in complete failure. A few issues that may occur with the 6.7 Cummins turbo include:

• Leaking oil seals
• Worn bearings (too much shaft play)
• Sticking VGT parts
• Compressor or turbine wheel damage

As turbos age, leaking oil seals and worn bearings are among the most common issues. B6.7 Cummins turbos run in excess of 100,000 RPM’s. Over time, the 6.7 turbo bearings may wear down and lead to excessive shaft play. If left alone the turbine or compressor wheel may contact the turbo housing and result in complete failure.

Since turbos run off incredibly hot exhaust gases it’s important to allow the oil to reach operating temperatures before pushing the Dodge Ram 6.7 Cummins too hard. Cold oil splashing on hot turbo seals is a recipe for premature turbo seal problems. You should also let the truck idle for a couple minutes before shutting down the engine. This will help cool the turbo.

Turbo problems can pop up at any point, but it becomes much more common north of 120,000 miles. A turbo rebuild may be possible. However, if your 6.7 Cummins is high mileage on the original turbo it may make sense to replace the entire turbo.

Turbo Failure Symptoms

Look for the following symptoms that may indicate an issue with the B6.7 turbo:

• Slow spool
• Poor performance
• Excessive smoke from exhaust
• Whining sounds

There are a few other possible symptoms, too. A sudden failure will typically result in drastic amounts of smoke and oil loss. Moderate smoke will also occur when the turbo seals are on their way out. 6.7 Cummins turbos failing over time will generally make whining sounds, spool slowly, and not reach the target boost.

Turbo Replacement Options

New OEM turbochargers come in north of $1,000 and often close to double that price. A remanufactured turbo will run around $1,000 to $1,500. It’s certainly not cheap. You can find some high quality 6.7 Cummins turbo upgrades for around the same price as OEM, if not even cheaper.

Turbo upgrades are a good route to go – in our opinion. It will allow you to extract a little more performance from your Dodge or Ram truck. However, turbo upgrades are still a good option even if you want OEM performance. A larger, more efficient turbo will have an easier job and should in theory hold up longer than the OEM turbo.

3) Heater Grid Bolt Causing Engine Failure

The heater grid on the 6.7 Cummins has a bolt on the bottom side of it that holds a metal conductor in place. Heat causes this bolt to melt which can then cause it to either break off or loosen the stud and completely fall out. When this happens it gets sucked into the intake manifold and then into the cylinders causing complete engine failure.

This issue is becoming more common as these engines get older – so far it has only happened on 2007.5-2018 models. The failure rate isn’t known but this can easily lead to $20k+ of repairs so the problem is very serious.

We’ve written a full guide on heater grid bolt failure and upgrades you can make to prevent the issue in a separate article. It’s worth a look and highly recommended to address this issue immediately to prevent it from happening as it can happen at any time and cause almost immediate failure.

4) Head Gasket Problems

Head gasket problems on the 6.7 Cummins may not be too common in actuality. However, compared to the previous 5.9 Cummins engines the B6.7 runs into the issue a lot more frequently. Part of it may have to do with the sheer power and torque the Dodge Ram 6.7 makes. High cylinder pressures may be to blame for the head gasket failures.

Chances are head gasket failures are somewhat blown out of proportion. In other words, it’s likely not as common as some may suggest. It’s still worth the mention though since head gasket replacement can be pretty pricey. When the head fails some opt to upgrade the fire-rings and head studs to help keep the head from lifting.

Head Gasket Failure Symptoms

• White’ish smoke with sweet smell
• Oil mixed with coolant
• Coolant mixed with oil
• Overheating

A blown head gasket will likely allow coolant into the combustion chambers. This will result in white smoke from the exhaust with a sweet smell from the coolant burning. Additionally, blown 6.7 Cummins head gaskets can allow oil and coolant to mix together. Higher pressure in the cooling system can also result in rapid overheating and/or coolant pouring out of the tank.

Replacement Options

Replacement costs can vary depending upon the year and model of the Dodge or Ram truck in question. Fortunately, there is only one head gasket thanks to the straight-six design. 6.7 head gaskets run in the ballpark of $100-200. Labor is where the costs begin to add up, and the repair can come in excess of $1,000 all in. That’s also assuming you’re not upgrading any parts.

Some 6.7 Cummins owners look to kits like this ARP head stud kit to avoid any potential issues in the future. The kits are expensive, especially when you add in labor. If you’re looking for a less expensive alternative, we recommend at least upgrading to the ARP head studs.

5) Fuel Dilution Issues

Alright – we’ll speed things up a bit moving through these next sections. Some fuel dilution in the oil is natural on the 6.7 Cummins engine. It’s inherent due to the way the engine manages regeneration. This is the process in that particulates are trapped in the DPF and burned for cleaner emissions. The 6.7 Cummins does not use a 7th injector to introduce fuel into the exhaust. Rather, the fuel injectors spray some fuel into the exhaust stream during the cylinders exhaust strokes.

This allows small amounts of fuel to stick to the cylinder wall where fuel can then mix with the oil. Some fuel dilution occurs in almost all diesel engines. However, some 6.7 Cummins diesels seem to have too much dilution. Dodge and Ram state the acceptable limit at 5% dilution.

Anything higher can be an issue since too much fuel can interfere with oils job to properly lubricate and protect the engine. It won’t cause any immediate and severe damage on the ISB 6.7L engine. However, it can result in premature wear for engine internals.

Symptoms

There aren’t usually any immediate symptoms of fuel dilution on the 6.7 Cummins. As such, it’s a good idea to do an occasional oil analysis. This will help you determine the rate of fuel dilution in your specific B6.7 diesel. You can then come up with an oil change schedule based on that information.

How to Avoid Fuel Dilution

A few ways to help prevent too much fuel dilution on the B6.7 Cummins include:

• Allow engine to warm up
• Avoid extended idling

Allow the engine to warm up before driving under heavy engine loads, such as towing heavy weights. The fuel is less likely to stick to the cylinder walls on a warmer engine. Additionally, avoid idling the engine for extended periods of time. This somewhat ties into point one. If the Cummins 6.7L diesel is left to idle too long the cylinder temperatures drop. This will increase the amount of fuel sticking to cylinder walls.

6) EGR Cooler Failure

EGR issues are a problem among many modern diesel trucks. The B6.7 Cummins is no exception here. It’s true most modern diesels primarily have issues with a lot of the emissions related equipment. As such, long-term diesel owners are likely well aware of these problems. We’ll keep this pretty short.

The EGR valve and cooler on the 6.7 Cummins is known to have problems, especially with higher mileage. It’s common for owners to simply delete the EGR system when problems do pop up. Of course, EGR delete can have legal concerns due to emissions laws.

Sometimes cleaning the EGR valve will help alleviate issues. Though, it’s usually a good idea to replace or delete the parts – especially if your Dodge or Ram 6.7 is higher mileage.

Dodge Ram 6.7 Cummins Reliability

Is the Dodge and Ram 6.7 Cummins engine reliable? Yes and no. The 6.7 diesel certainly doesn’t have the same reputation as some of the older diesels like the 5.9 Cummins or 7.3 Powerstroke. However, many modern diesel engines are in the same boat as the 6.7 Cummins. A lot of the emissions related technology can really kill these diesels. DPF and EGR problems are a few of the emissions parts that can cause headaches on the 6.7 Cummins engine.

That said, the 6.7 Cummins is a fairly reliable engine overall. This is especially true if you opt to delete some of the emissions equipment like the DPF and EGR systems. Beware of potential emissions or legal implications, though.

Otherwise, maintain your B6.7 Cummins well and it will likely reward you with a solid, reliable experience. It’s a good idea to perform the occasional oil analysis to confirm fuel dilution. Work out an oil change schedule based on the results. Keep up with other basic maintenance and stay on top of repairs as 6.7 Cummins failures occur.

Again, the 6.7 Cummins may not have the same legendary reputation as some of the older diesel engines. When well maintained the ISB 6.7L should still hold up well beyond 250,000 miles. We’ll consider that pretty respectable longevity.

Summary

The Dodge, Ram ISB 6.7L Cummins is an impressive diesel engine. It was the first light duty truck to break into the 1,000 torque territory with the 6.7 Powerstroke following shortly after. There’s no question the 6.7 diesel provides plenty of power and torque for almost any owner. However, no engine is perfect and this applies to the Cummins 6.7.

It’s mostly emissions equipment that brings the engine down a little bit. EGR and DPF problems are common on the 6.7 Cummins – as well as many other modern diesels. The sheer torque of the 6.7L engine can also cause issues with the head gaskets failing. Otherwise, turbo problems are possible with higher mileage as they take a lot of abuse. Fuel dilution is also another area that can be an issue, but the occasional oil analysis will help mitigate the risks of dilution of the oil.

Dodge and Ram trucks with the 6.7 Cummins engine are pretty reliable, overall. Sure, it doesn’t have the same legendary reputation as older diesels like the 7.3 PS or 5.9 Cummins. Unfortunately, the emissions parts of the modern day work against reliability in many ways. Nonetheless, maintain the 6.7 Cummins well and it shouldn’t have any issues eclipsing 250,000 miles.

What’s your experience with the 6.7L Cummins straight-six?

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