A smooth transition
In strenuous applications, the engines run hot enough to “passively” clean the CPF. For lighter work, a “dose” of misted diesel fuel injected upstream of the CPF “actively” creates the heat necessary for cleaning. The driver will not notice this. Even in the mildest, coolest-running applications, the system will use less fuel than a night of idling. Ash from burned oil additives collects in the CPF, and it takes about an hour once every two or three years to vacuum it out.
Cummins’ testing showed about the same or slightly better fuel efficiency as the pre-’07s, and improved reliability and durability.
My test began on U.S. 31, heading south from Columbus on Cummins’ 100-mile test drive route. The route includes city and rural driving, and two- and four-lane roads. It has flat land and genuinely challenging hills, particularly the narrow, 6-percent drop on state Hwy. 446, complete with hairpin curves, down to Lake Monroe (during which I was more concerned with safety than testing) the mile-long, equally steep climb back up, and the half-mile, 8 percent climb up “Kelly Hill,” just west of Nashville, Ind., on state highway 46.
It was sunny and clear. Pat and I chatted, but outside of town we soon encountered some 3- and 4-percent hills, a few of which were more than a half-mile long. I employed my standard torque/horsepower test formula: braked hard on the descents and started each climb in high gear at about 1,250 rpm and 50-55 mph: no running starts, just muscle. This is neither standard operating procedure nor the most effective way to drive a big truck, but it shows what an engine’s made of. The ISX chugged nonchalantly along, and I never had to drop a gear until we climbed up from the lake, where I dropped to 17th, and up Kelly Hill, where I dropped to 16th.
We got back, took a break, and then I climbed into the ISM test truck: an ’05 KW T600 with an ’07 ISM rated at 410 horsepower and 1,550 pounds-feet of torque, an Eaton 10-speed automatic and 3.90 rears. We hauled a 40-foot, drop-deck flatbed. Including myself and Technical Specialist Ryan Hedgecomb, my companion for the ISM drive, we weighed about 59,500 pounds. The CPF was horizontally mounted beneath the cab, just about directly below the passenger’s seat.
The ISM test drive was, if anything, smoother and even less eventful. The Eaton 10-speed shifted up and down as necessary. To more thoroughly test the engine’s power and torque, I locked in high gear and started the climbs at about 1,250 rpm and 50-55 miles an hour. The Eaton automatic would’ve dropped a gear had I let it. But like the ISX, the ISM pulled its load in high gear up all the hills except two without strain or complaint. As we climbed from the lake, the Eaton downshifted to ninth, and climbing Kelly Hill it dropped to eighth.
Upon returning to Cummins, I learned that the “dose” of misted diesel fuel does not “burn” the particulate matter collected on the filter. It creates heat sufficient for a chemical reaction that converts carbon soot and nitrous oxide to harmless carbon dioxide and nitrogen. The filter does not get hot enough to start a fire under the truck.
It sounds unusual, but the really big news was that I didn’t notice anything about the performances of the ISX and ISM that set them apart from other engines. They pulled just as hard and steady as, if not more than, their Cummins predecessors or any equally rated heavy-duty diesels. If the CPF actively cleaned itself with the “dose” of misted fuel, I never knew, nor would any driver.
Cummins is poised to produce the ISX and ISM engine and drivetrain combinations to customer specs, whatever they might be. Limited production begins this fall and will ramp up to full capacity next January.