A well-maintained Cummins in a Ram heavy-duty pickup commonly reaches 300,000 to 500,000 miles or more before needing major engine work, and many go further. The Cummins inline-six owes its reputation to a heavy block, a gear-driven camshaft, a simple layout with fewer moving parts than a V8 diesel, and conservative factory ratings. How long a specific Cummins lasts depends mostly on maintenance, air and fuel filtration, and how hard it has been used or modified.
How long each Cummins lasts
| Engine | Reputation | Watch for |
|---|---|---|
| 5.9 12-valve (1989 to 1998) | Very durable and simple, mechanical injection | Killer dowel pin on some engines, lift pump |
| 5.9 24-valve (1998.5 to 2002) | Durable | VP44 injection pump failures, some cracked “53” blocks |
| 5.9 common rail (2003 to 2007) | Durable | Injectors, lift pump, fuel quality |
| 6.7 (2007.5 on) | Durable core engine | Emissions system upkeep, injectors, turbo; see 6.7 Cummins problems |
See 5.9 Cummins problems and Cummins generations for years and versions.
What makes a Cummins last
- Oil and filter changes on schedule with diesel-rated oil; see 6.7 Cummins specs for capacity.
- Clean air: a sealed intake and a good air filter.
- Clean fuel: filters changed and water separators drained; see water in diesel fuel.
- A healthy cooling system and proper warm-up before heavy load.
- Reasonable power levels: big increases add stress to pistons, head gaskets and the transmission.
Signs of a worn Cummins
- Excessive blow-by; see diesel blow-by
- Oil consumption and smoke; see diesel white smoke and diesel black smoke
- Hard starting and low compression; see diesel hard to start when cold
- Knocking that rises with load; see diesel knocking
Buying a high-mileage Cummins
Mileage alone says little. Ask for maintenance records, look for blow-by at the oil fill, check for coolant or oil leaks, listen for knocks and look at the exhaust on a cold start. On 6.7 trucks, ask about emissions system service history. A compression or blow-by test from a diesel shop gives a clearer picture than the odometer.
The rest of the truck often wears out first
On many high-mileage Cummins trucks, the transmission, front end and body need attention before the engine does. Heavy towing is especially hard on automatic transmissions; see 48RE problems and 68RFE problems.
When it is time
If the engine is worn out but the truck is solid, a replacement engine is often the practical choice; see what comes with a long block, engine replacement checklist and our Cummins engines. For diesels in general, see how long do diesel engines last?
More guides: Cummins killer dowel pin · Cummins head gasket · how long a 68RFE lasts.
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