Test drive evaluates International HX with S13 engine

Engineers cut weight from the T14 by using a single countershaft (vs. the common dual-shaft), and its reverse ratios are accomplished with a planetary gearset instead of flat gears, Hanson said. As many as six reverse ratios are available for special applications, but Navistar ships the transmissions with just two unless more are requested.

Allison torque-converter automatics can be spec’d for applications where there’s a lot of stopping and starting. A special engine rating of 370 horsepower and 1,250 lb.-ft. is available for use with lower-cost Allison 3000 series transmissions, while heavier and higher-priced 4000 series versions can be fitted to higher-power engines.

For vocational use, the T14 has several special functions that the driver can use. Among them: Rock Free, to extract a truck from mud or loose soil; Maneuver, for creeping with a crawler gear in tight quarters; and Manual, to hold a gear and lock out an up- or downshift, except to protect the engine from overrevving and “grenading.”

There’s also Hill Start, which keeps brakes applied while stopped on an up-grade for up to three seconds. In that time, the driver needn’t worry about the rig rolling backward and simply presses the accelerator to resume moving. Clutch engagement is smoother than most drivers could do with a manual clutch and tranny. (Competitors’ AMTs offer these features, too.)

Power take-off drives can be fitted to an engine’s front and rear, and a transmission’s rear and sides, using industry-standard mounts. This tractor’s T14 had a dual-drive PTO at its rear, at 4 o’clock, alongside the main output shaft for the driveline.

The engine’s Jacobs compression brake can make up to 470 retarding horsepower, enough to seriously slow the rig on short but steep downgrades on the proving grounds’ gravel trail. The Jake is controlled by pulling down on the selector stalk behind the steering wheel, from Off through three positions. On steep downgrades, revs rose to 2,000 and 2,100 to extract maximum performance. 

Embracing SCR

The S13 diesel has double overhead camshafts and four valves per cylinder. Otherwise, Hanson said, it’s relatively simple, with a fixed-geometry turbocharger and wastegate instead of a complex (and costly) variable-vane turbo. There’s no EGR cooler, which is a troublesome part in many diesels. Exhaust-gas recirculation is still used, but not much—a far departure from the sadly unsuccessful EGR-only MaxxForce diesels.

Instead, the S13 employs two-stage selective catalytic reduction (SCR), using diesel exhaust fluid that chemically neutralizes oxides of nitrogen, a principal target of emissions regulations. There is no “seventh injector” because extra fuel does not keep the aftertreatment system warm; hot exhaust gas does.

Clean-burn combustion squeezes as much energy as currently possible from fuel and little soot is produced, Hanson said. As with other diesels, soot from fuel and ash from motor oil is collected by a diesel particulate filter. It’s boxed with the SCR chamber, but the S13’s DPF cannot be cleaned; instead, it must be replaced. Intervals are long, from 450,000 miles for vocational engines to 650,000 miles for highway engines running at 8.2 mpg or more. 

Including the 370-horse version, there are six vocational ratings of the S13, all with torque curves tailored for on/off-road operations. You can now order the new engine in the HX, and it eventually will appear in other vocational models. Of course, on-road ratings of the S13 are available in highway trucks and tractors.

Notably, Navistar says this is the last internal combustion engine it will offer, as development is now concentrated on zero-emission powertrains, meaning battery-electric and fuel cell-electric vehicles. It predicts that by 2030, half the trucks it sells will have electric propulsion and by 2040, all of them will. That’s a ways away, but time flies; so if you’re wary of that e-future, better grab an S13 or another diesel while you can.