Cummins Diesel Guide
The inline-six durability legend.
The Cummins B-series — the 5.9L and later 6.7L turbodiesel in Ram (and earlier Dodge) trucks — is the engine that built the modern diesel-truck following. Unlike the V8 competition, it's an inline-six: mechanically simpler, with one cylinder head and one valvetrain, and a reputation for running far past the truck around it.
That simplicity and a famously stout bottom end are why well-maintained Cummins engines routinely top 300,000 miles, and why it has the deepest aftermarket of any diesel. Most Cummins trouble at higher mileage is emissions-related — the turbo, EGR, and DPF — rather than the long block giving up.
Stout bottom end
The Cummins long block is famously durable; the engine often outlasts the rest of the truck. Failures are usually bolt-on systems, not the block or rotating assembly.
Emissions are the weak point
On the 6.7, the variable-geometry turbo sticking, EGR cooler/valve failures, and DPF clogging on short-trip trucks are the most common issues — manageable with maintenance and highway miles.
5.9 vs 6.7
The pre-emissions 5.9 is prized for simplicity; the 6.7 adds DPF/EGR (and later SCR/DEF) but more power. Both are durable when cared for.
Huge aftermarket
If you tow or want more power, no diesel has more support — but big power still needs supporting mods like EGT monitoring, head studs, and a capable transmission.
Cummins guides
Common Cummins trouble codes
Cummins — frequently asked questions
Is the 6.7 Cummins reliable?
Yes — the long block is famously durable and runs very high mileage. Most 6.7 issues are emissions-related (turbo, EGR, DPF) rather than bottom-end failures.
How many miles will a Cummins last?
Well-maintained 6.7 Cummins engines routinely exceed 300,000 miles, and lightly-stressed examples often outlast the truck around them. The 5.9 has a similar reputation.
What are the most common Cummins problems?
On the 6.7: sticking VGT turbo vanes, EGR cooler and valve failures, DPF clogging on short-trip trucks, and at higher mileage some head-gasket seepage and worn injectors.
Got a Cummins? Talk to a specialist.
Get a technician who knows the Cummins on the line — they'll interpret your symptoms and codes in context before you buy parts.
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