In August 2008, the truck maker decided to tackle EPA's 2010 emissions rules with its proprietary EGR-only solution, the MaxxForce 13 and 15 engines, and the (soon-to-be) SCR-equipped ISX was delisted for U.S. and Canadian 2010 model-year trucks.
But Cummins and Navistar didn't exactly remain strangers. The company continued building ProStar+ trucks with EGR-only ISX and ISM engines for the Mexican market, along with other chassis configurations and various Cummins engines in markets around the globe.
An easy fit; the pre- and post-2010 ISX aren't much different externally.
Navistar announced in July 2012 that it would discontinue its EGR-only approach and bring SCR-equipped Cummins ISX engines back into databooks by the spring of 2013, reuniting the ISX and the ProStar+.
Tom Smith, director of ISX/SCR integration at Navistar, told us they had a few dozen pre-production trucks in customers’ hands for trials and testing before Thanksgiving. The first batch of nearly 300 fleet-ready trucks began rolling off production lines in January and February.
“The ISX with SCR is a mature and proven product,” Smith says. “We did not need to spend a great deal of time in technology development, but we did spend several months in validation and durability tests as well as customer satisfaction trials. We had to make it feel like the powertrain had been in the truck all along.”
Which of course, it had, just not in the U.S. or Canada. Adding the SCR aftertreatment device and the DEF tank was not a large undertaking, Smith says.
“The DEF and fuel tanks were a bit of a challenge,” he admits. “Customer surveys indicated they wanted the DEF tank on the left-hand side of the truck, since that is where most on-island DEF pumps are. We switched the position of the battery and storage boxes with the fuel tanks. The standard DEF tank position is behind the battery box, with the DPF/SCR module under the right-hand door where a storage box used to be. The fuel tanks are now aft of the cab under the sleeper.”
A drop-in solution
Thousands of ISX-equipped ProStar+ trucks were produced prior to Jan. 1, 2010, so it was a matter of dusting off the old plans and shelving, for the time being anyway, the parts needed to make the MaxxForce 13 fit between the frame rails.
The switchback aftertreatment package is trucked beneath the passenger door, close to the turbocharger to maintain high exhaust temperatures at the catalyst.
Externally, there's not a great deal of difference between the pre- and post-2010 ISX engine, but the addition of the aftertreatment module caused a few things to be pushed around on the ProStar+ frame to make room for it. Still, it boasts a pair of 26-inch, 120-gallon fuel tanks and a 23-gallon DEF tank, so little was given up there.
Actually, moving the tanks back beneath the sleeper solved one challenge we saw on previous ProStar+ models: steer axle weight.
With the ISX coming in roughly 500 pounds heavier than the MaxxForce 13 engine, they really had no choice. According to the spec sheet, this ProStar+ weighs 10,565 pounds dry. That is no oil, no fuel, no DEF, etc. It's worth noting that the truck comes with a 14,000-pound front axle and load-range H tires.
The product brochures say the MaxxForce 13 weighs 2,400 pounds dry, while the ISX 15 comes in at 2,964 pounds dry plus 220 pounds for the aftertreatment module.
According to Smith, however, this configuration is actually lighter up front than the tanks-forward MaxxForce set-up.
The Cummins ISX will be available in ratings of 400, 425, 450, 485, 500, 525 and 550 horsepower, with 1,450, 1,550, 1,650 or 1,850 pounds-feet of torque.
Out on the road
As you may have gathered from the photos, our test drive wasn't exactly a walk in the park for the ISX.
The five-axle trailer we pulled, courtesy of Nationwide Freight Systems of Brantford, Ontario, was loaded with bags of cement and tipped the scales at 122,460 pounds.
Our test engine was rated at 485 horsepower and 1,850 pounds-feet, so the load was perhaps a bit disproportionate for the rating. But there are fuel-conscious fleets in Canada pulling that kind of weight with less-than-500-horsepower engines.
The cockpit is familiar territory, except for the DEF tank level gauge.
It's all about the torque, really, and that certainly wasn't lacking at 1,850. One thing is certain, exhaust temperatures would help to keep the regens to a minimum.
I had a couple of hours with the truck, so I ran it on some two-lane roads as well as some four-lane divided interstate-type highways. I drove it over the Burlington Bay Skyway Bridge and up what the locals call the Clap-pison Cut on Hwy. 6 near Hamilton, Ontario.
It's a nasty 7% climb that begins at the bottom of a freeway off ramp, which means you hit the bottom of the hill with the brakes on. It's pedal to the metal the rest of the way up.
I came off the freeway in 6th gear, eased through the turn and before I could gain any rpm at all, the grade pushed me down into the low side of the gearbox. I was into 3rd gear before I knew it and slogging my way up.
Midway up, the grade levels to about 4%, where I snuck in an upshift. A bit risky, but at 1,800 rpm, I figured I had time to stuff it into 4th gear before gravity dragged me to a stop.
Wrong. I barely got it back into 2nd gear in time after realizing 4th was out of the question. I managed two upshifts on the shallower grade before cresting the hill.
The engine fan came on mid-way up the hill at 210 degrees, and remained on until the crest in our sub-15-mph, high-output pull. I have to say it was darned quiet, despite the 1,500-rpm engine speed.
Despite that bit of excitement, the rest of the drive was predictable and uneventful. The ISX cruised like a champ at 1,500 rpm at 62 mph. With peak torque at 1,200, there was plenty of wiggle room on the modest freeway grades.
The 23-gallon DEF tank sits on the left-hand side between the battery box and the fuel tank.
Upshifting in the low side of the Eaton Fuller 18-speed was accomplished at less than 1,000 rpm with ease, and on the high side, I was close to 1,700 a few times, but most of the upshifts were at 1,500 or less. Bottom line, it's a good economical engine in the right hands.
This was the second EPA-2010 configured Cummins ISX I have driven in the past year, and I can honestly say there were no differences in performance. I can't speak to regens or fuel economy in either case because I had the trucks for only a few hours each.
Anyone who is used to and happy with the ProStar/ Cummin ISX in pre-2010 trim will be happy with what has emerged from the reunion of these two industry favorites.
Nothing really new. No surprises. Just the power and performance you'd expect from a 15-liter engine once again wrapped in the ample creature comforts of the ProStar+.
Truck: 2014 ProStar+ 6x4 Sleeper
Engine: Cummins ISX485 hp/1,850-lbs.-ft.
Transmission: Eaton Fuller RTLO(F) 18918B 18-speed manual with double overdrive, double low
Front axle: Hendrickson Steertek NXT 14,000 lb.
Tires: Michelin XZA3+ 275/80R22.5 Load range H
Steering: TRW (Ross) PCF60
Rear axle: Meritor MT-40-14X4DER-P, 3.90:1 ratio
Suspension: International Ride Optimized (IROS) 52-in. spread 40,000 lbs.
Tires: Michelin XDA3 11R22.5 Load range G
Aftertreatment: Horizontal switchback, under right-hand door
BBC: 122 in.
Wheelbase: 230 in.
Dry weight: 18,258 lbs. (calculated)