The 6.7 Cummins is the most reliable diesel pickup engine you can buy, with a bottom end that regularly passes 500000 km. Watch the CP4 pump on 2019 and newer models, fix the grid heater bolt on 2007 to 2022 models, and change fuel filters on time.
- Block, crank, and pistons are overbuilt and routinely last 500000 km
- CP4 pump on 2019 and up models is the main risk, a failure costs around 10000 dollars
- Grid heater bolt on 2007 to 2022 models can destroy the engine, cheap aftermarket fix exists
- 2013 to 2018 is the sweet spot with the proven CP3 pump
- Fuel filter changes are the single most important maintenance item
The 6.7 Cummins has a reputation as the most reliable diesel pickup engine you can buy. After fourteen years of working on them, I will tell you straight: the reputation is mostly earned. But "reliable" does not mean "nothing ever breaks." Here is what I actually see in the shop.
The bottom end is bulletproof
The block, crank, rods, and pistons on a 6.7 Cummins are overbuilt in a way the competition is not. It is an inline six derived from medium duty commercial engines. I have seen these with 500,000 km on the original bottom end, still running strong. If you maintain it, the core engine will outlast the truck around it.
What actually breaks
Fuel system. The CP4 injection pump used on 2019 and newer Rams is the weak spot. When a CP4 fails, it sends metal through the entire fuel system. That is injectors, rails, lines. A $10,000 repair. The older CP3 pump (2007.5 to 2018) is far more forgiving. If you own a 2019+, run a fuel additive with lubricity and change your fuel filters on schedule. Every time.
Emissions equipment. DPF, EGR, DEF system. Same story as every modern diesel. The 6.7 is not worse than others here, but it is not exempt either. Trucks that tow regularly have fewer problems than trucks that idle around town.
Grid heater bolt. On 2007 to 2022 models, the grid heater bolt in the intake can loosen, fall in, and destroy the engine. It is rare but catastrophic when it happens. There is a simple aftermarket fix. If you own one of these years, look into it.
Transmission. This is not the engine, but it matters: the 68RFE automatic behind many 6.7s is the weak link when you add power or tow heavy constantly. The Aisin in the high output models is a different animal and holds up much better.
Model years, ranked by what I see
- 2007.5 to 2012: Simple, tough, CP3 pump. Higher mileage examples are fine if maintained. Watch for rust, not engine problems.
- 2013 to 2018: My pick for the sweet spot. CP3 pump, proven emissions systems, comfortable trucks. The ones I see with the fewest complaints.
- 2019 and up: More power, nicer interiors, CP4 pump. Great trucks, but budget for fuel system vigilance.
The honest verdict
If you want a diesel pickup that starts every morning in minus 30 and pulls a trailer without drama, the 6.7 Cummins remains the safest bet in the segment. Just go in with your eyes open about the CP4 on newer models, delete the grid heater worry with the aftermarket fix, and do not skip fuel filter changes. Do those three things and this engine will take care of you.
Frequently asked questions
Is the 6.7 Cummins reliable?
Yes. It has the strongest bottom end of the big three diesels and the fewest catastrophic failure modes. The CP4 pump on 2019 and newer models is the one real worry.
Should I buy a 6.7 Cummins with high mileage?
If the maintenance history is good, yes. These engines outlast the trucks around them. Check for CP4 service records on 2019 and up, and ask if the grid heater bolt was addressed on 2007 to 2022.
What is the best year for the 6.7 Cummins?
2013 to 2018. You get the reliable CP3 pump, sorted emissions systems, and comfortable trucks. The 2019 and up trucks are nicer but carry the CP4 risk.