If you've spent any time around diesel trucks, you've definitely heard people venting about common 6.7 Cummins problems while standing around a tailgate or browsing a forum. Don't get me wrong—the 6.7 is a legendary workhorse that's been the heart of the Ram Heavy Duty lineup since mid-2007, but it's definitely got its quirks. Whether you're looking to buy one or you've got one sitting in your driveway right now, knowing what usually goes sideways can save you a massive headache down the road.
Most of these issues aren't because the engine block itself is weak. In fact, the iron is stout as ever. Most of the "gremlins" come from the stuff bolted onto the engine—specifically the parts designed to keep the air clean.
The Elephant in the Room: Emission Systems
Let's be real: the biggest headache for most owners involves the Diesel Particulate Filter (DPF) and the Exhaust Gas Recirculation (EGR) system. Since the 6.7 Cummins had to meet much tighter emissions standards than the old 5.9, it's basically breathing through a straw and then inhaling its own soot.
The DPF is designed to catch soot, but if you only use your truck for short grocery runs and never let it get hot enough to "regen," that filter is going to clog up. When it clogs, your fuel economy hits the floor, and you might find your truck in "limp mode." The EGR valve is another culprit; it gets caked in carbon over time, which can lead to rough idling or even a check engine light that just won't stay off. If you aren't working the truck hard, these common 6.7 Cummins problems show up much faster.
The VGT Turbo Soot Issue
The 6.7 Cummins uses a Variable Geometry Turbocharger (VGT). It's a cool piece of tech that helps the truck reach peak boost faster and even provides exhaust braking. But here's the catch: the sliding nozzle inside the turbo can get stuck.
Why does it stick? You guessed it—soot. If carbon builds up on those moving parts, the turbo can't adjust properly. You'll notice the exhaust brake stops working, or the truck feels sluggish because it can't build boost correctly. A lot of guys try to fix this by "exercising" the turbo (basically driving it hard) or using the exhaust brake every time they drive, which actually helps keep those parts moving. If it gets too bad, though, you're looking at a pricey turbo replacement.
The "Killer" Grid Heater Bolt
This is one of those problems that keeps people up at night. It doesn't happen to every truck, but when it does, it's catastrophic. Inside the intake manifold, there's a grid heater that helps the engine start in cold weather. It's held together by a nut and a bolt that can, over time, vibrate loose or corrode.
If that bolt falls off, it goes straight into cylinder number six. Since there's zero room for a chunk of metal in a high-compression diesel engine, it usually results in a complete engine failure. Many owners end up installing an aftermarket "wiggle-proof" solution or a completely different intake plate just to avoid this specific disaster. It's a small part, but it's arguably one of the scariest common 6.7 Cummins problems out there.
Fuel System Drama: The CP4 Pump
If you own a 2019 or 2020 model, you probably already know about the CP4 fuel pump saga. For a couple of years, Ram switched from the old reliable CP3 pump to the Bosch CP4. Long story short, the CP4 didn't handle American "dry" diesel fuel very well.
When these pumps fail, they "self-destruct" and send tiny metal shavings (basically glitter) through the entire fuel system. That means you aren't just replacing a pump; you're replacing injectors, lines, and the fuel tank. It's a multi-thousand-dollar nightmare. Thankfully, there was a massive recall, and most of these have been swapped back to the CP3 style, but if you're buying a used 2019-2020, you need to check if that recall was performed.
Head Gaskets and Heavy Tuning
The 6.7 Cummins is a beast, and it's very easy to add a tuner and some bigger injectors to make insane power. However, the stock head bolts weren't really designed to handle 60+ PSI of boost.
Even on stock trucks, head gasket leaks can happen if the engine is consistently overheated or pushed way past its limits. If you see white smoke or notice you're losing coolant with no visible leaks, you might be looking at a head gasket job. Most guys who plan on "cranking it up" will swap out the factory head bolts for heavy-duty studs as a preventative measure. It's a "pay now or pay a lot more later" kind of situation.
The Plastic Water Pump
It's almost funny that such a heavy-duty engine relies on a water pump that has historically had some plastic components. Around the 2013-2017 year range, there was a significant issue with water pumps failing prematurely. Some of them would leak, while others would actually catch fire if the bearing failed and the belt kept spinning against it.
Replacing the water pump is actually a pretty easy DIY job, and most people swap in a high-quality unit with a metal impeller the moment they see a drip. It's a minor annoyance compared to a blown engine, but it's definitely one of those common 6.7 Cummins problems that can leave you stranded on the side of the highway if you aren't paying attention to your temp gauge.
Keeping the Fuel Clean
Diesel injectors are incredibly sensitive to dirt and water. The 6.7 uses a high-pressure common rail system that operates at pressures that would literally cut through skin. If even a tiny bit of water gets past your filters, it can ruin an injector.
Worn-out injectors usually show up as a "haze" from the tailpipe or a rough idle. Because they're so expensive to replace, most veteran Cummins owners are religious about changing their fuel filters every 10,000 to 15,000 miles. Some even add an extra aftermarket filtration system (like a FASS or AirDog) just to be safe. It's cheap insurance for a very expensive engine.
Is the 6.7 Still Worth It?
After reading through a list like this, you might be wondering if you should just buy a gas truck and be done with it. But here's the thing: despite these common 6.7 Cummins problems, people still swear by them. Why? Because when they're running right, there's nothing quite like the torque and pulling power of an inline-six.
Most of these issues are preventable with the right maintenance or a few strategic upgrades. If you keep your cooling system healthy, change your oil and fuel filters on time, and maybe keep an eye on that grid heater bolt, these engines can easily go 300,000 miles or more.
It's not about finding a "perfect" engine—those don't exist. It's about knowing what to watch for. If you stay ahead of the soot and the sensors, the 6.7 Cummins will probably outlast the rest of the truck it's sitting in. Just don't ignore the warning signs, and she'll keep pulling whatever you hook up to the hitch.