Juiced Up

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Medium-duty diesels are growing up. Nowadays, most of them are as sophisticated-or nearly so-as their heavy-duty brethren. They sport electronic controls that bring new features and capabilities previously unknown in the mid-range world. The motivation for that change is in part the demands of emissions regulations, as well as the truck owner’s wish for fuel economy.

Beyond that, however, is the necessity to integrate engines with the equally sophisticated new crop of automatic or automated transmissions. For example, Freightliner Corp. president Jim Hebe says his company is working with an unnamed transmission manufacturer-his hints suggest an offshore supplier-to bring an all-new mid-range automatic box to North America. It will be an electronic full automatic, meaning it will have a torque converter, to be mated with engines from the Cummins ISB on up-or for gross weights up to about 26,000 pounds. Hebe offers no predictions as to timing, but says he’s anxious to have it because current drivetrain component manufacturers can’t meet the demand.

Eaton Corp., meanwhile, is about to bring the same sort of automation to its existing medium-duty mechanical transmissions that has proved so successful in its heavy-duty offerings. Arguably, a relatively inexpensive, mechanically simple semi-automated gearbox is even more useful in mid-range trucks than in heavies.

That development depends entirely on electronics and on data communications links between engine and transmission-the two must talk to one another if their operation is to be so closely integrated that the transmission is going to tell the engine when to de-fuel, for example. The resultant efficiencies-and driving ease-can pay big dividends in a market where drivers are often not truckers first.

What follows here is a brief review of engine developments at each manufacturer represented in the Canadian market, as well as a spreadsheet listing basic specifications, model by model. We’ve defined “medium duty” broadly here, in the interest of thoroughness: some of these engines, such as Caterpillar’s C10, Cummins’s ISM, or Detroit Diesel’s Series 50, are in fact used in the light-heavy market; others, such as Ford’s gas engines, are used in trucks well below that level.

Note that Navistar is about to announce developments in its engine line, and there will soon be a range of engines from Daimler-Benz arriving on these shores, some of which will fit into the market discussed in this article. We should have details for you soon.


Gone from the Caterpillar lineup are the 3116 (both mechanical and electronic versions) and 3176 medium-duty engines, as well as the vocational 3306C. The mid-range flag is now flown by the much revamped 3126B, a 7.2-litre diesel that now offers more of the electronic features of bigger Cats-programmable progressive shifting, coolant monitoring, and full PTO control are all recent additions.

Existing electronic features included “SoftCruise” speed control, for example, a programmable option that modulates fuel delivery above and below the set cruise speed to eliminate annoyingly abrupt fuel cutoff.

There’s also password protection, theft deterrence, and an idle shutdown timer.

All new Cats feature a faster 32-bit processor. The electronic control module now supports up to 140 inputs and outputs and, more importantly, the SAE J1939 communications protocol. This is what allows integration with the latest automated mechanical transmissions that work in tandem with the on-engine controller.

Other changes made last year to the 3126 include new injectors and higher injection pressures, which allowed Cat to meet 1998 emissions regulations-by better fuel control-without needing exhaust aftertreatment.

As well, a new three-valve-per-cylinder crossflow head improves gas flow and lowers heat rejection for improved turbo performance.

The 3126B is available in ratings from 175 to 300 horsepower (330 for fire trucks), with torque ratings from 420 to 860 pound feet.


There’s been an enormous amount of activity in Columbus, Ind., over the last two years as Cummins has redesigned its entire engine line. From the very willing little 5.9-litre ISB (175 to 250 horsepower) to the 8.3-litre ISC (215 to 300) and on up to the very new 8.9-litre ISL (310 to 350), the medium-duty truck buyer’s wishes are well covered.

Introduced in 1997 as a much revamped version of the Cummins B-Series, the ISB features a 24-valve head and full electronic controls that bring programmability and easy diagnostics. They also allow the engine to fit into the company’s “Interact” system. In a nutshell, that’s a Cummins concept-really a strategy-that aims to integrate the engine’s electronic controls with other truck systems and with the fleet’s broader business system, delivering information to driver, dispatcher, or fleet manager. In essence, if the truck is a local-area network (or LAN), that broader system is a wide-area network (or WAN). There are also previously introduced software tools such as Inform, Inspec, and Insite that serve the manager and technicians as part of the system. The ISB was the first Interact engine.

Other ISB features: wastegated turbocharger, 15,000-mile oil-drain intervals, SAE J1939 datalink capability, and light weight (it’s just 962 pounds).

The ISC, which arrived on the scene not long after its smaller brother, is also a 24-valve, in-line six with full-authority electronic controls. It’s targeted as much at the bus and motorcoach markets as trucking. It features a totally new electronic fuel system and wet-sleeve, mid-stop cylinder liners to make overhauls faster and easier.

The newest Cummins, the ISL, was introduced last year and isn’t yet fully on the market (production started this past January, and so far only the 330-horse rating is available, with 310, 350, and 370 coming by year end). It has the same innovative injection system as the ISC and takes over from the discontinued mechanical L10-while weighing some 600 pounds less and adding the benefits of sophisticated electronic control.

Like the ISB and ISC, it has the 24-valve head, no-adjust overhead cam, and low-maintenance fuel filters, plus automatically tensioned accessory belt and rear engine PTO. It also has mid-stop cylinder liners like the ISC and 18,000-mile oil drains. Options include the Jacobs-designed C-Brake and the Centinel engine-oil management system.


There will be bigger news soon by way of an all new 14-litre engine from Detroit Diesel, but it’s pretty much status quo in the 8.5-litre Series 50 line. Not, strictly speaking, a mid-range engine, the four-cylinder, overhead-cam Series 50 is in fact two thirds of a 12.7-litre Series 60-with the middle two cylinders removed. As such, it sports all the sophistication of “DDEC” electronics, but it’s no lightweight. It has gear-driven, counter-rotating balance shafts said to make it run as smoothly as the bigger six.

Available in seven ratings for this year, from 250 to 320 horsepower and 800 to 1150 pound feet of torque, all of them are rated at 2100 rpm. That’s a change from last year, when there were 1800-rpm ratings as well, but DDC says the engine can be just as fuel-efficient if the proper gearing is employed-not to mention proper driving. Interestingly, the engine is one of the few to utilize ceramic components-in the injector rocker arm’s cam-follower roller and, for lower inertia, in the turbine wheel.


The three engines in Ford’s class-3 to class-6 lineup include the 5.4-litre V8 and 6.8-litre V10 gas engines, plus the Navistar-built 7.3 litre and Cummins 5.9-litre diesels.

The V10 and 7.3 diesel are available in the F-450 and F-550, with three GVW ratings at 15,000, 17,500, and 19,000 pounds. Those two engines also offer, uniquely, an optional PTO with the new 4R100 automatic transmission. There’s also a new six-speed manual box for the 7.3.

Power and torque are up slightly in 1999 for the gasoline engines (rated at 235 and 275 horses respectively, with 335 and 410 pound feet of torque).

The class-6 F-800 truck gets either a mechanical or electronic version of the 5.9-litre Cummins diesel, with ratings from 175 to 215 horsepower, depending partly on the transmission choice you decide to make.


There are two new gas engines from General Motors, the Vortec 7400 MD and Duramax 7800, but we’ll see only the former in Canada. The other change in GM’s trucks is the disappearance of the Caterpillar 3116 diesel, replaced by the redesigned 3126B for this year.

The 7.4-litre Vortec 7400 is the only gas engine you’ll see in a class-5-or-bigger medium-duty truck, being available in the venerable GMC C-Series conventional. In two ratings (210 and 270 horsepower), it offers electronic fuel control, which brings engine- and road-speed governing, PTO capability, and optional engine shutdown protection. The 210-horse version develops its peak torque of 325 pound feet at a commendably low 1200 rpm (unique in a gas engine) with a very flat torque curve between 1000 and 3200 rpm to boot. The 270’s peak torque is 405 pound feet, but it comes on at 3200 rpm in a less useable steep curve. The Cat 3126B is also available in the C-Series truck as well as being the only engine choice in the T-Series cabover.


The only Japanese truck manufacturer doing business in Canada, Hino introduced a new product line a year ago and made only minor changes for the 1999 model year. The entry-level FB truck (GVW at 17,600 pounds) has the J05C-TB engine, a turbocharged four that benefits slightly from some emissions tweaking-it gained three horsepower (up to 168) and four pound feet of torque (up to 166). Those gains came by way of new injectors and adjusted timing.

We road-tested the 1998 version of this truck/engine combo, and said the new 5.3-litre engine makes for a quick little truck. It’s a sophisticated piece of work, a big four-valve overhead-cam design, and like its six-cylinder brother (the J08C-TD, for class-6 and -7 trucks) it features electronic timing control and a standard exhaust brake. Both noise and vibration are reduced in these new engines, as well as internal friction, so the package is quieter, smoother, more fuel-efficient, and more powerful-with no weight penalty. Not incidentally, filters and other consumables are from standard North American suppliers.


It’s status quo at Mack as far as the Mid-Liner’s engines are concerned, though the MS cabover truck was redesigned for the 1999 model year. The two engine choices are 190 and 220-horsepower versions of the 6.2-litre E3 in-line six, made by Mack’s parent company, Renault. It’s turbocharged and charge-air cooled, and at 1090 pounds it’s a lightweight.


The three engines that Navistar builds for its mid-range trucks are now fully changed over to electronic controls. The T444E V8 and the DT466E, and 530E in-line sixes got a single black box last year (there had been three separate engine control boxes). They also gained rate-shaped fuel injection for better emissions control and lower noise.

The company is working on the next generation of its diesel engines that will go into Ford light trucks in the year 2003, a six-litre V8 and its derivative, a 4.5-litre V6. They’ll use a variation on the HEUI fuel system with its hydraulically actuated injectors, but with new high-speed digital valve technology that could find its way into bigger International engines soon.

Navistar, like others around the world, is also working on a hybrid engine, and it showed a working example in a chassis last year at a Society of Automotive Engineers gathering. It was a combination of a T444E diesel engine, a generator, a set of lead-acid batteries, and an electric drive motor in a United Parcel Service package car. By no means a new concept, the hybrid idea means low emissions, which makes it very attractive as a short-term environmental solution.

Navistar says it uses between 20% and 40% less fuel than a diesel alone. The 175-horse diesel drives a 120-kW generator that in turn charges the 23 batteries and feeds current to the induction drive motor.

That motor draws battery power for acceleration, while cruising under 100 km/h is the diesel’s job. While it’s running, the diesel brings the batteries back to full charge. The drive motor acts as a retarder during braking, returning current to the batteries while it does so.

There’s little doubt that such hybrid powerplants will be part of the medium-duty truck’s future, and in fact Navistar’s version is close to production. Three test units are in fleet use now.

Get used to the idea. If you’re running mid-range trucks in urban duty, chances are you’ll have hybrid power sooner than you think. After that phase is over, think fuel cell.

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Rolf Lockwood is editor emeritus of Today's Trucking and a regular contributor to Trucknews.com.

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