Navistar's 2010 Diesels Keep Their Cool

Sept. 28, 2010
International WorkStar

Verbal skirmishing between Navistar International and its competitors over their two paths toward meeting new exhaust emissions limits has included charges that Navistar's 2010 diesels will run hot. Not so, the company has declared, and it recently offered proof to trade-press editors. Engineers put some of us into several International trucks for a driving experience, and we saw that their '10-model MaxxForce engines were energetic but cool performers, at least under cool and wet conditions.

Higher levels of exhaust-gas recirculation — part of Navistar's Advanced EGR system for 2010 — will surely make the engines run hotter and rot their innards, said competitors, who also run EGR and will continue to, but not as much as Navistar. The company's ride-and-drive event dismissed some of the fear over hot running, though time will tell about effects on longevity.

The Chicago-area event happened as unseasonably cold and wet weather covered much of the United States (whatever happened to Global Warming?). Under these conditions engine heat shouldn't be a problem, period. But Navistar engineers said the enhanced cooling modules in their trucks work just as well under more extreme conditions, and they promised us later experiences in hotter weather.

For now, my conclusion is that Navistar might just have something with these A-EGR diesels, and the company will be a real contender in sales wars against competitors with their selective catalytic reduction-equipped 2010 diesels. That's based on drives of two International trucks: a medium-heavy duty WorkStar with the midrange MaxxForce DT, and a ProStar tractor with a MaxxForce 13, which will be Navistar's biggest engine for a while into 2010.

Water-temp gauges in both vehicles stayed at an almost constant 180 degrees F throughout my runs, causing me to accuse ride-along engineers of gluing the gauge's needles in place. They laughed and denied it, explaining that cooling systems are designed to extract excess heat from the engines and dissipate it into the atmosphere. And the systems also do that under hot and high-altitude conditions, though then the gauges might show 200 degrees or more. About 10 million miles of lab and road testing has been done on each engine series, which includes the smaller MaxxForce 7 V-8 and the MaxxForce 11, another big-bore engine.

Lou Maza, a senior project engineer, directed me on a 2-hour, 40-mile tour through some of Chicago's northwest suburbs in the WorkStar. This model often does construction duties, but this truck had been spec'd as a development test bed for use by Navistar engineers. That explains its highway oriented Eaton Fuller 10-speed manual transmission where an 8LL would usually be found. Maza explained that this tranny is likely to be pulled and replaced with others over the truck's life. Good riddence, I'd say, because I seldom made an up- or downshift without some gear crunching and a "thunga-thunga-thunga" sound in the clutch linkage below the floor.

But, of course, the point of the truck was the engine, and it behaved just fine. The much refined 6.4-liter diesel had the highest rating of 300 horsepower and 860 pounds-feet, so it ably moved the 30,000-pound truck (16,000 pounds of chassis and 14,000 pounds of concrete blocks on a flatbed body) away from the many red lights we encountered along boulevards and semi-rural highways. At first I used a light foot and every gear beyond 3rd, which was low enough for starting on level pavement, but acceleration was way too slow. After a while I put my foot into it and skip-shifted in Low range to get us up to speed more quickly.

The engine would rev as high as I wanted, but its official redline was 2,400 rpm and I usually up-shifted sooner, at 2,000 to 2,200 rpm, and cruised at 2,000 and 40 to 45 mph in 9th. At low revs the engine didn't complain, but seemed happier closer to 2,000, which was a good point from which to speed up and slow down with traffic. A few times I got it into 10th gear on highways and tollways, where road speed was as fast as 65 mph. Combined power and torque ("porque"?) seemed almost completely even throughout the usable rev range, with no "lighting up" at any point on the tachometer.

As I said, the water temperature gauge stayed right at 180 degrees F throughout the trip, and with no help from the fan. It was the same story in the ProStar sleeper-cab tractor, with its 475-horsepower, 1,700-lbs.-ft. MaxxForce 13. This one had a Fuller 13-speed, which I was able to operate easily. In 8th-High (the 13th ratio) and 65 mph, the engine loafed along at under 1,300 rpm, right where it should be for top economy, said my rider, Mike Regula, director of Navistar's big-bore engine program.

My ProStar drive was brief, but enough to show that its cooling system kept water, and the engine, at a constant and low temperature, again aided by cool ambient temps and rain splashing on the radiator cores. The month before, the trucks' cooling modules also worked well in high-altitude tests west of Denver, along I-70 through the Eisenhower tunnel (11,158 feet above sea level) and on Loveland Pass (11,900 feet) on a twisting stretch of U.S. 6, Regula related. Thin air up there makes engines run hotter and heat exchangers less effective, but the modules did what they are supposed to.

On both medium- and heavy-duty trucks, a 2010 module includes a large, two-core radiator, an air-to-air charge air cooler and an air conditioning condenser. Most MaxxForce diesels will be double-turbocharged, and big-bore versions will have a water-to-air cooler between the two turbos, as do current models, while midrange diesels won't need the inter-turbo cooler. Exhaust gas on midrange models runs through a single-pass cooler before going to the intake manifold, while big-bore engines use a two-pass gas cooler.

In a morning briefing before our drives, engineers led by Ramin Younessi, group vice president for product development and strategy, explained the features of the engines themselves. A-EGR is far more than EGR because Navistar's 2010 diesels will also have enhanced combustion-chamber design, more capable electronic controls, and very high-pressure fuel injection, he said.

There'll be considerable weight advantages — 300 to 400 pounds because Navistar will avoid SCR and its heavy and bulky equipment, and another 500 to 600 pounds if Navistar customers who prefer big-bore diesels will buy the idea of choosing a 13-liter model instead of a 15. They'll have to for six to eight months into the new year, because the new MaxxForce 15 won't be ready for a while.

Competitors have been calling Navistar's Advanced EGR rates "massive," but they're not, Younessi insisted. A-EGR will run no more than a 37 percent exhaust-gas rate at the intake manifold, with the other 63 percent being clean air, and the rate will average about 25 percent. Recirculated exhaust gas displaces oxygen and cools combustion, which lowers formation of NOx. Navistar's rates are only a few percent higher than competitors' 2010 diesels using EGR as well as SCR. Fuel economy will be as good or better than current Navistar engines, and improved aerodynamics on ProStar highway tractors will make them even more competitive, he said.

A silly question for a Navistar engineer is whether these engines will hold up in day to day service for a long time, but I asked it of Lou Maza anyway. "Absolutely," he declared. "Sure, these are our products, but from what I've seen, they're doing very well." Testing in labs and in Navistar's own trucks has covered many millions of miles, Younessi had said, and MaxxForce-powered vehicles will soon be in customers' hands for their own trials. Those and experience in coming years will truly tell the tale.

WorkStar and its load of concrete blocks together weigh about 30,000 pounds. It has a 14,000-pound steer axle, a 40,000-pound tandem and — oddly for this kind of truck — a highway oriented 10-speed gearbox. Engineers explained that this truck is a test bed that will get other transmissions during its life in Navistar's test fleet.
Under the hood, the midrange MaxxForce DT is hidden behind turbos, pipes, filters and a fluid bottle. Cooling module includes two-core radiator.
Water-temp gauge (left of the tach) on the WorkStar stayed at 180 degrees and edged just above that at the end of a sub-urban run, showing the MaxxForce DT was running cool.