While diesel has always struggled to find a mainstream user base here in the US, Americans who drive diesel engines tend to swear by them. The low-end torque offered by diesel and the durability of these engines are big pluses, and, as gas prices continue to rise, diesel's superior fuel economy is more helpful than ever.
If you're looking for a diesel-powered pickup that might well last you the rest of your life, your best bet is going to be a heavy-duty Ram with a Cummins under the hood. We reported a while back on a Ram 3500 with more than two million miles on the odometer, far outrunning the highest-mileage Toyota Tundra or Toyota Tacoma. Here's what makes the Cummins-powered Ram 2500 and 3500 pickups such troopers.
A Cummins Ram Could Tow A Mountain
The 5.9 ISB Cummins-powered Heavy-Duty Ram 2500 (not to be confused with the earlier 5.9 6BT-powered 1989-1998 models) ran from 1998 until early 2007, with a 2006 model having a towing capacity of 13,600 lbs. The 3500 was available with dual rear wheels, and can tow up to 16,250 when properly equipped.
| 2006 Ram HD Cummins Performance Specs | |
| Engine | 5.9-Liter Turbodiesel 6-Cylinder |
| Power | 325 hp |
| Torque | 610 lb-ft |
| Transmission | 5-Speed Automatic |
| Drivetrain | Rear or All-Wheel Drive |
Both trucks pack the exact same engine, with the difference in pulling power coming down to the suspension setup in each truck. Towing capacity actually peaks in the 3500 Rams. The 4500 and 5500 both sacrifice some pulling power for their heavier frames and suspension systems. A fully outfitted 5500 doesn't just tip the scales, it crushes them, weighing in at over 10,000 lbs.
Cummins Rams Are Still Going Strong
The 2026 Heavy-Duty Ram pickup is available with a more powerful 6.7-liter Cummins diesel, another straight-six B series, like the 5.9 before it.
| 2026 Ram HD Cummins Performance Specs | |
| Engine | 6.7-Liter Turbodiesel 6-Cylinder |
| Power | 430 hp |
| Torque | 1,075 lb-ft |
| Transmission | 8-Speed Automatic |
| Drivetrain | Rear or All-Wheel Drive |
For 2026, when properly equipped, the 2500 tops out at 20,000 lbs of towing capacity, with a maximum payload capacity of 3,930. The 3500 can tow up to 36,610 lbs, with a maximum payload capacity of 6,050 lbs. The 6.7 Cummins has been powering turbodiesel Rams since the 2007 model year.
A 5.9 ISB Cummins Might Last Forever
You really can't go wrong with any Cummins-powered Ram. Epictechwill, on the I Got A Cummins forum, reports clocking an incredible 1.3 million miles in a 2014 Ram 3500 with a 6.7 powerplant. That's probably more miles than you put on your last three cars combined. But it's nothing next to the 5.9-powered 2000 Ram 3500 belonging to RV deliverer Howard Clayton.
Clayton had put an incredible 2,687,028 miles on his truck at the time we ran that story, driving an average of 700 miles per day to deliver RVs all around the country. The most surprising thing may be that Clayton was putting oil changes off, skipping the recommended every-3,000-miles intervals and making a stop at the mechanic every 10,000 miles for fresh oil.
As Clayton explains it, sticking to the recommended timeline would have had him stopping into the shop nearly twice a week, which just isn't practical. We would have recommended changing it himself, but hey, he's the one with the 2-million-mile Ram, not us. The head gasket went out at 1.7 million miles, there have been some oil leaks over the years, and the engine has undergone a rebuild, but, at over two million miles, it's almost beside the point to bring any of that up.
| 2000 Cummins 5.9 ISB Engine Specs | |
| Displacement | 5,883 cc |
| Bore | 4.02 Inches |
| Stroke | 4.72 Inches |
| Compression Ratio | 17.2:1 |
Ram's partnership with Cummins dates back to the 1989 model year, when the Ram was made available with a 160-hp 5.9, cranking out 400 lb-ft of torque. Dodge had been struggling to sell Mitsubishi diesel-powered trucks to Americans, with limited success, and the Cummins turned out to be the missing piece of the puzzle.
The B-series has been around since 1984, with the 5.9 engine using a cast iron block and head with a forged steel crankshaft with seven main bearings, and a forged aluminum intake manifold. The ISB is a multi-valve pushrod engine, packing four valves per cylinder, lending it the nickname "24-Valve" Cummins. The Dodge Ram made the jump to the ISB midway through the 1998 model year in order to keep up with emissions requirements.
Sources: Stellantis, I Got A Cummins, RepairPal.
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This article originally appeared on CarBuzz and is republished here with permission.
