5 Common 6.7 Cummins Engine Problems

The 6.7 Cummins is an excellent engine that can deliver up to 420 horsepower and 1,075 lb-ft of torque. However, all engines are prone to the occasional failures and the 6.7L diesel is no exception. Some of the most common issues include the DPF, EGR cooler, heater grid bolt, turbocharger, and fuel dilution. In this article, we discuss these 6.7 Cummins diesel engine problems in-depth.

6.7 Cummins Diesel Engine Problems

  • Clogged DPF
  • EGR Cooler
  • Heater Grid Bolt
  • Turbocharger
  • Fuel Dilution

Many 6.7 Cummins problems revolve around emissions equipment. Unfortunately, the days of engines like the 5.9 Cummins and 7.3 PowerStroke are long gone. Emissions are an important part of keeping diesels on the road today, but many of these parts have been known to be problematic. Anyway, let's jump in and discuss the above problems in greater depth.

1) Clogged Diesel Particulate Filter (DPF)

A clogged diesel particulate filter is one of the most common issues on the Ram 6.7 Cummins - especially engines built before 2013. Initially, Cummins did not use diesel exhaust fluid (DEF) which means the engine must run a little rich to reduce NOx emissions. However, running a diesel engine richer increases soot. In turn, the additional soot can quickly clog the DPF.

DPF problems were so bad early on that Dodge and Ram rolled out numerous PCM adjustments to mitigate the issues. In 2013, SCR and DEF were introduced to help reduce particulates (soot). Ultimately, 2013+ Ram trucks with the 6.7 Cummins experience DPF issues much less often. However, clogged diesel particulate filters do still occur and that's especially true at higher mileage.

Power loss, long cranking, fault codes, and reduced power mode are some of potential symptoms of DPF issues. If you're noticing these symptoms, it may be time to consider solutions to replace or clean your particulate filter.

6.7 Cummins DPF Replacement

The one major downside to 6.7 Cummins DPF problems is the cost of replacement. A new or refurbished DPF tends to run in the ballpark of about $1,500-2,500. Another option, which isn't always a good long-term solution, is pressure washing and cleaning the OEM DPF. Sometimes this can help clear up the DPF enough to get a couple extra years of use.

2) EGR Cooler Issues

Problems with EGR systems and coolers are popular among many modern diesel engines. Unfortunately, this also applies to the B6.7 Cummins. EGR stands for exhaust gas recirculation and, as the name suggests, the system circulates exhaust gases back through the engine. Of course, exhaust gas is extremely hot so that's where the EGR cooler comes into play.

Both the EGR valve and cooler are common faults on the 6.7L Cummins. When the cooler fails it allows coolant to leak into the cylinders, which causes white smoke and steam from the exhaust. This may lead some to misdiagnose EGR issues as a head gasket failure. Additionally, coolant entering the engine can cause serious issues if it's not addressed in a timely manner.

EGR Cooler Replacement & Upgrades

As with a clogged DPF, fixing a 6.7 Cummins EGR cooler or valve can be an expensive repair job. If it's the valve, then simply cleaning it may be an effective solution. However, EGR coolers often fail due to cracks so a replacement is necessary.

There are proven aftermarket solutions for both the cooler and valve. Bullet Proof Diesel offers some excellent upgrade options that make problems much less likely in the future. Their EGR cooler upgrade comes in at $1,245 while the EGR valve kit will set you back $767.

3) Heater Grid Bolt Failure

For those less familiar with diesel engines, the heater grid (along with exhaust fluid and numerous other things) may sound like some random made up thing. The heater grid is located on the intake manifold and increases the temperature of the air as it passes over. The purpose of the heater grid is exactly the same as the glow plugs: to warm the air during cold starts and cold engine operation.

The 6.7 Cummins heater grid contains a bolt on the bottom side that holds a metal conductor in place. Over time, this bolt is prone to failure due to fatigue from heat cycles. Why are we talking about issues with one measly, inexpensive bolt?

Well, the bolt is inside the intake manifold so failures ultimately lead to the bolt being pulled into the engine. It can then cause serious damage to pistons, cylinder walls, valves, etc. Best case you're left with a cylinder that needs a complete rebuild or you may be left with complete engine failure.

Heater grid bolt failures are primarily seen on 2007.5-2018 trucks. We aren't aware of any issues with 2019+ engines. Anyway, the bolt failure doesn't show any symptoms before failure so inspecting the bolt and taking preventative measures is the safest option.

Preventing Failure of the 6.7 Cummins Heater Grid Bolt

The first option is simply inspecting the bolt every couple years to ensure it still looks good. However, this isn't always the safest option since you may not see any signs of fatigue cracks or other issues with a visual inspection. As such, the best ways to prevent 6.7 Cummins heater grid bolt failure are:

  • Weld the bolt in place
  • Grid heater delete
  • Intake manifold & grid heater upgrades

Welding the bolt in place is the cheapest and simplest option to ensure the bolt in securely in place for the longer-term. Grid heater deletes are another possible option, but it's not always a recommended option. Remember, the grid heater aids in cold starts so deleting it may give you trouble. Lastly, upgrading to an aftermarket intake manifold and grid heater can offer some performance benefits on top of ensuring a reliable 6.7 Cummins.

4) 6.7 Cummins Turbo Failure

Turbocharger failure is one of the less common problems we're discussing in this article. Modern turbos tend to be very reliable despite the constant abuse. However, diesel engines also have long lives and partially rely on high boost to make massive torque. In other words, the 6.7 Cummins puts a lot of stress on the turbo and can also outlast the useful life of a turbocharger. Some common causes of turbo issues include:

  • Leaking seals
  • Worn bearings
  • Sticking VGT components

In rare cases, the 6.7L Cummins may experience premature turbo failure. However, issues often occur north of 120,000 miles when the turbo is naturally beginning to get a little "tired" due to natural wear and tear.

Symptoms of turbo failure often include slow spool, whining sounds, smoke from the exhaust, and poor overall performance. It's possible to rebuild the 6.7 Cummins turbo depending on the exact failure and the extent of the damage.

5) Fuel Dilution Problems

Last but certainly not least are 6.7 Cummins fuel dilution problems. Fuel dilution refers to diesel fuel diluting the engine oil. Some fuel dilution in the oil is natural and simply boils down to how the engine handles regeneration. Particulates are trapped in the DPF and then burned off for cleaner emissions via diesel fuel injection.

Diesel engines may use an extra fuel injector to spray fuel into the exhaust. The 6.7 Cummins does not use an extra injector, though. Instead, the injectors spray fuel into the exhaust stream during the cylinders exhaust stroke.

In turn, some excess fuel can stick to the cylinder wall where it's then picked up by the oil. Dodge and Ram state 5% dilution is an acceptable limit for the 6.7L diesel. Additional dilution can be a serious problem as it affects the oils ability to properly lubricate and protect the engine. It's not going to kill the engine overnight. However, excess fuel dilution over the long-term can have negative impacts on internal wear and longevity.

How to Avoid Fuel Dilution

  • Oil analysis
  • Allow engine to warm up
  • Avoid excess idling

An oil analysis doesn't directly help negate fuel dilution. However, oil analysis allows you to determine the rate of fuel dilution and set an oil change interval accordingly.

Otherwise, allow the engine to warm up before doing any spirited driving or towing heavy loads. Fuel is less likely to stick to cylinder walls on a warmer engine. Also, avoid idling the engine for extended periods.

6.7 Cummins Reliability

Writing about common engine problems can sometimes paint a dreary picture and make an engine appear less reliable. As such, it's important to tie everything together and discuss 6.7 Cummins reliability.

Despite some common issues, the 6.7 Cummins is still a reliable diesel engine. Sure, it's not as reliable as some of the old-school diesels like the 5.9 Cummins or 7.3 PowerStroke. A lot of it simply boils down to modern emissions equipment which comes with a number of reliability issues and drawbacks. However, the 6.7L Cummins isn't alone here; nearly all the modern diesels have suffered the same or similar issues.

Ultimately, it doesn't have the same legendary reputation as its older brother - the 5.9 Cummins. However, it's still a great engine. With proper maintenance and repairs, most 6.7 Cummins engines can hold up well beyond 250,000 miles

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