Equipment Type

SCR’d MaxxForce 13 Now a Joy To Drive

Navistar changed course on exhaust emissions controls by adopting selective catalytic reduction, and it also improved engine response

June 27, 2013

Navistar is attemping a turnaround on two fronts—its financial woes and its engines—and a drive of its revised heavy-duty diesel offerings strongly suggests pleasing progress. The driving was during a show-and-tell for trade-press writers where executives and engineers described more efficient development and manufacturing operations at their Melrose Park, Ill., engine facility. I came away impressed by a new confidence among executives that has replaced the defiance and competitor-bashing we saw and heard from previous execs. And I liked the performance of their engines.

For several years, Navistar went its own way on diesel exhaust emissions, dealing with nitrogen oxide strictly in its engines’ cylinders and resisting the use of urea injection, the active component of selective catalytic reduction. SCR is what all its competitors in North America and most others around the world had chosen, even though it adds weight and bulk to a truck. But Navistar’s engineers couldn’t lower NOx enough to meet absolute government limits. Meanwhile, expensive problems with the flagship large engine, the MaxxForce 13, caused sales to drop, profits to erode, and stock prices to plunge.

A revolt led by major shareholders caused Navistar’s top executives to change horses, dropping exhaust-gas recirculation and embracing SCR. Financial losses required cutting costs by cancelling and selling a number of engine and truck-building programs. The upheaval also saw a change in top management, including the promotion to president and CEO of Troy Clarke, a former General Motors engineer and executive who had joined Navistar a short time before. Clarke, an approachable and affable guy, led the low-key cheerleading at the ride-and-drive event near the company’s headquarters in Lisle, Ill., in late May. 

He and his team showed off the two big-bore diesels now offered in Class 8 International trucks and tractors: Navistar’s own 12.4-liter MaxxForce 13 and Cummins’ 15-liter ISX, which replaces the MaxxForce 15 that’s now gone after only a few were built. Both current engines have SCR. Once banished from domestic trucks because of its SCR approach, Cummins is once again Navistar’s partner. Cummins sent engineers to Melrose Park and Lisle to help in the transition to SCR, and now supplies the ISX15 as well as emissions-reduction equipment for Navistar’s own diesels, starting with the MaxxForce 13.

Though they spoke glowingly about Cummins, their own engine is what Navistar execs are pushing hardest. There’s more potential profit, not just through engine sales but with parts and service business for the manufacturer and its dealers. During this event, I drove four tractors—two of them with MaxxForce 13s and the other two with ISX15s—so we could feel the difference. Bigger is usually better, but this time the smaller Navistar diesels were more fun.

I started with an International 9900i long conventional, which has been one of my favorite models because of its classic looks, smooth ride, and pleasurable driving characteristics. However, this one proved difficult to drive because of a very hard clutch pedal and stiff gearshift lever connected to a fleet-spec Eaton 10-speed manual transmission. Better component choices, especially on this style of truck, would’ve been a power-assisted clutch and a 13- or 18-speed tranny. But I could feel the engine’s strength. This one was rated at 475 horsepower and 1,850 lb.-ft., so even at nearly 80,000 pounds gross weight, the rig was propelled smartly down the I-88 tollway.

Later, I got in a ProStar+ daycab tractor with an ISX15 mated to an Eaton UltraShift Plus, a self-shifter that made a world of difference. Now I could just use the accelerator and brake pedal as appropriate and steer the rig. And I could more fully appreciate its big Cummins, which had a curious rating of 425 horsepower and 1,700 lb.-ft. Torque was hefty, but why would someone buy a 15-liter engine with such modest power? For better resale value, our driving hosts suggested, because the engine could be uprated and made more attractive to a second owner. Some buyers will also prefer a 15 for pulling extra-heavy loads or in mountainous terrain, execs had said earlier. The ISX15 can be had with as much as 600 horsepower and 2,050 lb.-ft., compared to 500 and 1,700 for a MaxxForce 13.

And some truckers think a 14- or 15-liter diesel will be more likely to make it to a million miles without an overhaul, I recalled. Yet Navistar engineers claim their MaxxForce 13 has a B50 life of 1.2 million miles, meaning at least half the engines should reach that point without major maintenance. As the old saying goes, your results may vary. This size diesel has long been the norm for construction trucks, and with healthier outputs, 13-liter engines are more than sufficient to pull most loads in long-haul service. So truck builders who have them—which now is just about everybody—have been saying that 13-liter diesels are the future.

Navistar’s MaxxForce 13 is a good example, as the two I drove on this day made 450 and 500 horses and the maximum torque of 1,700 lb.-ft. And for anyone concerned with tare weight, executives said the 13 weighs about 500 pounds less than the ISX15, which makes up for the 400 or so pounds of SCR equipment that every Class 8 truck will have. Stated another way, a MaxxForce 13-powered International with SCR weighs 400 pounds more than before, but should be sweeter to drive and own.

That’s because going to SCR has allowed Navistar engineers to cut way back on the amount of exhaust gas returned to the cylinders. How much less depends on operating conditions, but 50 percent is a representative figure, engineers said. That’s notable because competitors coined the term “massive EGR” to describe how Navistar was trying to beat down NOx without urea injection. Dirty exhaust gasses muck up the EGR valves that regulate exhaust flow—even lighter doses do—and put high heat loads on cooling systems. These problems should be reduced.

Also reduced are issues with the diesel particulate filter, execs said. Since 2007, fleet managers have been complaining about cracked and plugged DPFs—from all engine makers, not just Navistar—but recalibrating the operating software has cut the number of active regenerations which consume fuel and stress the honeycomb substrate. On-road testing of MaxxForce 13s in a group of its own road tractors since January has covered more than 2 million miles, and higher-than-expected uptime has allowed it to be done sooner than expected. But as of late May, individual engines had each run only 125,000 miles at most, so longevity must still be determined. 

For now, fuel economy is better with SCR, something that competitors have been saying since 2010, because with NOx suppressed in the exhaust system, engines can be tuned for performance and economy.  “Substantially” is one adjective Navistar people used to describe the resulting economy, but they didn’t offer any numbers. Neither did they bring up “fluid economy,” the total of fuel and diesel exhaust fluid, which of course Navistar engines consume now. Henceforth, everyone will line up at the same two pumps. 

What is now obvious to a driver, though, is better throttle response than with pre-SCR MaxxForce 13s. This is what Troy Clarke told us writers before we drove the new engines, and this is what I found while driving two ProStar+ tractors with the MaxxForce 13s. Also, one of our hosts remarked that the ProStars drove nicer than the 9900i, and it was true. One of the ProStars had a 10-speed manual and the other a 13, and both shifted easily. So, as with the self-shifting transmission in the Cummins-powered ProStar, I could enjoy the engines.

One of the MaxxForce 13s was a 500 with a dual-torque 1,550/1,700 lb.-ft. rating, and the other made as much as 450 horsepower and 1,650 lb.-ft. And they were a joy: Step on the go-pedal and they went, right now. Acceleration was snappy at any road speed, and pulling power at low revs—1,000 rpm and less—was impressive. Several times, I found the tach at about 900 rpm and, rather than downshift, simply eased into the accelerator and the engine speeded up without complaint. Once I did this from 700 rpm, with the same results: no shaking, no missing, just torque that gradually built as revs climbed back into the operating range. To be fair, competitor 13-liter diesels will also do this, but Navistar’s seems to be livelier at 1,300 to 1,700 rpm.

One of my colleagues remarked at how quiet the Navistars were, and he was right. But I’d have preferred a little snarl to make things more entertaining. As far as a driving test, northern Illinois is pretty flat, and I wished for some hills to climb. Maybe another time. But at this point I have to say that the MaxxForce 13 with SCR is a lot of fun to drive, which drivers should like, and it ably does a hauling job, which managers will appreciate. If reliability and longevity prove to be as good as Navistar engineers and executives think, then this engine’s going to boost customer fortunes and that corporate turnaround.

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