While many diesel-engine enthusiasts are swayed by horsepower, performance and fuel-economy numbers, commercial operators typically look long and hard at another critical though less-sexy metric in their competitive analysis: maintenance needs.

That’s because the costs of upkeep, including such mundane chores as changing engine oil, can add up to a pretty penny over the life of a diesel engine.

And for some operators, it’s those numbers – and not the outlandish torque ratings – that win them over to a particular make and model.

Take the Cummins 6.7L turbodiesel powering Chrysler Group LLC’s Ram pickups, for example.

While it placed last in the Best Engines Diesel Shootout in acceleration times, compared with Ford Motor Co.’s home-grown Power Stroke and General Motors Co.’s Duramax, it nabs the top spot outright in terms of lower maintenance lifecycle costs.

While engine oil, fuel-filter and engine-coolant change intervals are almost the same among the three OEMs, diesel exhaust fluid (DEF) replenishment needs and life-to-overhaul metrics aren’t even close.

For starters, the Cummins engine uses an oxides of nitrogen catalyst to comply with exhaust emission rules, completely eliminating the need for the selective catalytic reduction technology used by Ford and GM.

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Diesel Shootout

That means no fill-ups of DEF, an ammonia-based liquid that is 67.5% water. DEF costs about the same as a gallon of diesel fuel, which is roughly $2.93 per gallon at the moment.

So, for Ford, that equates to $16.11 on average to refill its 5.5-gallon (21L) DEF tank, and GM comes in at $15.52 due to its smaller 5.3-gallon (20L) tank.

How many miles the truck is driven per year, of course, dictates how much DEF gets used annually. Trucks in heavy use will need several fill-ups annually.

From a big-picture perspective, life-to-overhaul is a critical figure both for those diesel owners planning to keep their trucks a long while and for used-truck buyers.

The Ram Cummins diesel offers far and away the longest interval here, boasting a 350,000-mile (563,255-km) life-to-overhaul timeline, while Ford comes in at 250,000 miles (402,325 km) and GM at 200,000 miles (321,860 km).

GM notes the 200,000 figure is calculated under the severest of operating conditions, so more sedate diesel owners might get more miles for that service interval.

Oil Change:

  • Ford: 7,500 miles (12,070 km)
  • GM: 7,500 to 10,000 miles (16,093 km)
  • Chrysler: 7,500 miles

Fuel Filter Change:

  • Ford: 22,500 miles (36,209 km); drops to 15,000 miles (24,140 km) if using B20
  • GM: 15,000 miles; drops to 10,000 miles if using B20
  • Chrysler: 15,000 miles, regardless of diesel-fuel blend

Engine Coolant Change:

  • Ford: Six years or 105,000 miles (168,977 km), whichever comes first.
  • GM: Five years or 150,000 miles (241,395 km), whichever comes first.
  • Chrysler: Five years or 100,000 miles (160,930 km), whichever comes first.

Diesel Exhaust Fluid Refill:

  • Ford: 5.5-gallon (21L) tank needs refilling about every 7,500 miles
  • GM: 5.3-gallon (20L) tank needs refilling about every 5,000 miles (8,047 km)
  • Chrysler: Uses a NOx catalyst so no DEF fluid required

Miles to Overhaul:

  • Ford: 250,000 (402,325 km)
  • GM: 200,000 (321,860 km)
  • Chrysler: 350,000 (563,255 km)