On paper, you can’t beat the Ram 2500 and 3500, equipped with the iconic 6.7-liter Cummins diesel engine. With 400 hp and 1,000 lb-ft of torque, it is an impressive package. And Ram has had great success with the Cummins engine since it was introduced in 2007. But being on the market for as long as it has, even with the improvements Cummins has engineered into it, common problems are well established. Let’s look at the five top problems with the Ram Cummins ISB 6.7-liter turbodiesel engine. 

Clogged diesel particulate filter or DPF on Ram Cummins engines

For the first few years, the 6.7-liter diesel was offered, Ram trucks didn’t use diesel exhaust fluid. That means for emissions reduction, it ran on the rich side. That, in turn, creates particulates, which is what clogs the DPF.

Ram was aware of the problem and recommended a number of PCM re-flashes to tame the issue. By 2013, Ram incorporated SCR emissions systems and diesel exhaust fluid. This reduced the particulates, which manifest as soot, but as the miles add up it is still a problem.

With the DPF chocked up, a cascade of issues can result. Back pressure is one because the exhaust gases can’t get out. That leads to heat issues as the engine works harder. You’ll know if this has affected your Ram truck if there is power loss, it takes longer to crank the engine, engine fault codes appear, or the power mode is reduced. 

You might wonder why you can’t replace the DPF filter like an oil or air filter. You can, but it is expensive. According to Diesel IQ, it can cost more than $1,000 for a refurbished unit. New ones are almost twice the price. 

Some Ram Cummins owners have opted to build a new exhaust system eliminating the DPF filter. That has proven a successful solution but has legal complications. To avoid a healthy fine, and to do your part in cleaning up your truck’s exhaust, the best solution is to replace the filter. 

Turbocharger failure on Ram Cummins engines

Turbochargers go through a lot of abuse. When heat and high speeds enter the mix, it is a recipe for failure. Turbos exceed over 100,000 RPMs. As the miles pile up, the turbocharger may start leaking oil seals, wear-out bearings, and damage VGT components and/or the turbo wheel. If the turbo wheel makes contact with the housing, it’s lights out.

One way to avoid premature turbo failure is to get the oil up to operating temperature before you hammer the throttle. Conversely, before turning the engine off, let it idle for a few minutes to allow the turbo to cool down. Turning off the Ram Cummins engine with the turbo so hot leads to problems. 

Blown head gaskets

With inherently higher compression in diesel engine cylinders, head gasket failure can be a problem. When you need the extra grunt is when the head gasket will most likely fail. Then, coolant can enter the cylinders. You’ll know if you notice white exhaust smoke. That’s steam, which means there is water in the mix. What’s worse is if the coolant contaminates the oil.  

The good news is that there is only one head, thus one head gasket. But the bad news is the cost to replace it. A gasket can cost between $100 and $200. The labor to replace it can top $1,000. 

Fuel dilution

The way the DPF works is that when particulates get trapped, they’re burned off. Fuel injectors introduce fuel into the exhaust stream. But that means fuel can get mixed into the oil. This is common with all diesel engines, but the Cummins 6.7-liter engines can see more dilution. Fuel in the oil results in more wear on engine parts. 

The best way to eliminate this potential problem is to let the engine warm up before operation and avoid long periods of idling. Keeping the cylinders warm helps to burn off any fuel that might stick to the cylinder walls. 

Cummins EGR valve and cooler issues

Higher mileage can result in EGR issues. Cleaning out the EGR will go a long way to keeping your Cummins happy. Or, replacing it might work better. However, a new EGR valve is costly, running over $1,500 in some cases. Some opt to delete the EGR system, but, again, there are legal and environmental issues dictating you don’t do this.  

Update: 6/20/2023