The 6.7 ISB is considered to be one of the most robust and reliable engines available in any HD truck, and it can last for 250,000 to 350,000 miles if properly maintained. In fact, many of the problems on the Cummins 6.7 in the 2010-2018 Dodge Ram 2500 and 3500 are DPF and SCR emissions-system issues and not with the engine itself. It gained a selective catalyst reduction (SCR) after-treatment system requiring diesel emissions fluid (DEF) in 2013, and the DEF must be replenished every 7,500 miles (see Maintenance and Cost).
The pre-2013 models before the SCR after-treatment system became standard do suffer more frequently from a clogged-up diesel particulate filter (DPF) because the engine has to run on a richer mixture to reduce nitrogen oxides in the exhaust gasses. This generates more soot that clogs up the DPF. Powertrain control module (PCM) flashes can be performed to improve the situation, but it seems that no amount of highway driving will prevent the DPF from becoming clogged at some point. The 2013+ models are far less likely to suffer this problem. Unlike some diesel engines, the 6.7 ISB does not use an additional injector to spray diesel into the exhaust to regenerate the DPF, instead using the existing six injectors to inject extra diesel, causing more fuel to adhere to the cylinder walls, which dilutes the oil in the sump. This problem can be circumvented by replacing the oil frequently, taking it easy while the engine is cold, and not idling it for extended periods.
The exhaust-gas recirculation (EGR) system's cooler will also eventually give up the ghost, as it does in most diesels, and because it's so expensive to replace, many owners delete the EGR system, as they do with the DPF too. This has legal implications and will cause your truck to fail its emissions test. EGR problems may be accompanied by the P0401, P0403, and P049d error codes. Problems with the DEF system on 2010-2018 Dodge Ram 2500 Tradesman/Big Horn/SLT/Laramie Longhorn and other trims with Crew Cab/Regular Cab/Mega Cab bodies and the diesel engine mostly have to do with the DEF pump failing and are reported fairly frequently, so check the dash for error messages.
In terms of the engine itself, head gaskets don't commonly blow, but it can happen, especially if the engine is allowed to overheat. Don't continue driving and have it fixed at once because if the coolant and/or oil level drops, engine damage is close at hand. Coolant and oil mixing also quickly compromises both the cooling and lubricating systems and will ruin the engine. The variable-geometry turbocharger caused quite a few issues in the early years of the 6.7 ISB, but is mostly sorted out on the 4th-gen Ram 2500. However, on occasion, oil seals may leak, the bearings may wear and allow too much shaft play (allowing the compressor or turbine wheels to contact the housing), the VGT blades may stick, and the turbo actuator may fail. These issues crop up more in neglected engines and are the exception, not the rule. Treating your turbo well by not making it work hard when cold, cooling down the engine properly before shutoff when it's hot, and replacing the oil frequently should prevent you from running into problems.
Overall, the 6.7 ISB is a tough motor, and the mechanical failures of the head gaskets and turbochargers mentioned here are exceedingly rare in well-maintained engines. The reason we mention them is because the engine works hard in an HD application, abuse is more likely, and repairs are a lot more expensive than on lowlier vehicles. Maintenance and frequent oil changes are very important, so you must insist on a full service history when buying used. The emissions equipment tends to cause problems, as they do in all diesels eventually, but in a case of a monster engine like the 6.7, everything is more expensive to replace. Neglected and modified engines are more likely to cause problems.
Mileage: A DPF may start clogging up from 100,000 miles. When present, turbocharger problems usually start at around 120,000 miles. Head gaskets usually fail due to usage patterns or overheating, not at a set mileage. There are hardly any Dodge Ram 2500 Cummins injector problems; these are reliable and last 200,000 miles. The odd turbo actuator has failed at around 70,000 miles.
Cost: If a DPF is beyond repair, replacing it will cost between $2,000 and $3,000, labor included. The DPF itself costs nearly $2,000, and even a refurbished one is likely to cost more than $1,000. Having the EGR cooler replaced will cost around $2,700. Having a head gasket replaced may cost as much as $2,600-$3,000. A replacement turbocharger costs up to $2,000, and a remanufactured one as much as $1,500; labor will be close to $1,000 in either case. Replacing a turbo actuator also costs close to $3,000 at a Ram dealer.
How to spot: A clogged DPF will lead to reduced engine power, poor running, slow starting, and fault codes. A blown head gasket may have many symptoms, depending on the failure mode. Some include a sweet coolant smell, smoke/steam from the exhaust, low coolant and/or oil, overheating, and engine failure. Turbocharger problems will usually cause power loss, a smoky exhaust, and whining sounds.