New heavy-duty Ram trucks feature Cummins diesel upgrades

  • 27-Sep-2012 12:00 EDT

Ram HD has an even bolder grille and a two-radiator front-end cooling module behind it.

Chrysler didn’t limit its 2013 truck line update to the new Ram 1500 pickup; it's following up with a new heavy-duty (HD) lineup. The 2500, 3500, 4500, and 5500 get upgraded versions of the 6.7-L Cummins six-cylinder diesel and a major change in the cooling system design.

The top-of-the-line diesel is rated at 850 lb·ft (1152 N·m) peak torque, which Chrysler claims is a class-leading figure, although tow and GCWR (gross combined weight rating) specifications have not yet been announced.

The HD line will go on sale in the first quarter of 2013.

Nine heat exchangers

The diesel cooling system uses nine powertrain heat exchangers, with seven in a front-end cooling module; the EGR and engine oil coolers, through which engine coolant circulates, are exceptions.

An A/C condenser is at the front, followed by an auxiliary radiator.  Next is an oil-to-air transmission oil cooler (TOC) mounted high in the module so it extends above the condenser and auxiliary radiator. Below it (behind the auxiliary radiator) is the power steering cooler. At the rear is the primary radiator, which also contains an oil-to-coolant TOC. A turbocharger air-to-air cooler (CAC), which is much wider than the others, mounts below the bottom line of the other heat exchangers in the stack, spanning the width of the oil-air TOC and primary radiator.

A new clutch type radiator fan completes the front-end cooling package. As with other heavy-duty trucks, it is electronically controlled. But it has higher performance, thanks to an increase from nine to 11 blades, and both fan and shroud are manufactured to tighter tolerances. The more precise manufacturing permits reduced clearance between shroud and blade tips, which minimizes airflow leakage, improving both performance and fan efficiency.

The two TOCs operate in series when oil temperatures are high. If not, a thermostatic bypass valve blocks the flow. The two radiators, supplied by Denso, are in a parallel coolant flow circuit, so they work effectively as one larger radiator, which wouldn’t fit. Overall heat rejection through the engine coolant radiators, oil-air TOC, and CAC is 25% greater in the 2013 model. This means lower air and fluid temperatures throughout the powertrain to meet an engineering bogey designed to improve durability.

Diesel details

The diesel, which accounts for about 85% of Ram HD sales, will be available in a range of horsepower and torque ratings, up to 385 hp (287 kW) and 850 lb·ft (1152 N·m). Fuel economy is 10% better, based purely on internal testing as there are no EPA numbers published for heavy-duty trucks and Chrysler doesn’t publish representative figures.

The improvement is largely from a high-pressure—1800-bar (27-ksi)—common-rail diesel injection system and the use of urea solution injection (exhaust fluid) with a new SCR (selective catalyst reduction) system for NOx control. The SCR after-treatment permits engine tuning for improved fuel economy.

The 2500 and 3500 have 8.0-gal (304-L) urea tanks and the chassis cab's has a 9.25-gal (352-L) capacity. The  tanks are electrically heated to keep the solution liquid in cold weather, a simpler approach than with lines from the engine cooling system.

The diesel has been approved for use with B-20 biodiesel, which results in reduced carbon emissions.

The diesels have a two-duct air intake. For normal operation, air is drawn from an underhood duct that runs to the fender well, and that also provides protection from ice, snow, heavy rain, and water if the vehicle is fording a stream. When the electronics sense extreme heat or a loss of engine power (as from low air density at high altitude), the intake at the grille opens to admit cooler air.

The diesel oil change interval was doubled to 15,000 mi (24,000 km). A new fuel filter, the high pressure common rail, and SCR-permitted calibration changes reduce fuel dilution and soot formation. The 2013 OE oil fill is a 5W-40 synthetic for the diesel in the HD trucks and a carryover 15W-40 oil in the HD chassis cabs. At the first oil change interval, the customer is free to choose either one.

Transmission, transfer case choices

A six-speed manual transmission model is still available. It is uprated to 660 lb·ft (894 N·m) from the 600 lb·ft (813 N·m) of 2012. The engine has a dual-mass flywheel, and the clutch is self-compensating for wear. A Chrysler six-speed automatic is mated to a 370-hp (276-kW), 800-lb·ft (1084-N·m) version of the Cummins.

An Aisin AS69RC six-speed automatic with a wide gear ratio spread for high efficiency and driveability is paired with the highest-output Cummins engine. A left-side PTO (power takeoff), or the capability of a split-shaft PTO, is available with this transmission.

The trucks offer a choice of BorgWarner part-time transfer cases, one electric shift, one manual shift. The four-wheel-drive models have a front-axle disconnect on the right side (long) shaft for improved fuel economy. An electric solenoid controls a clutch.

Upgraded electrical system

The diesel uses a smart charging system. A sensor to measure current flow into and out of the battery provides the primary signal for a load-shedding system that prevents the battery from running low. However, an optional second 220-A alternator is available for vehicles with high electrical content.

A new Vehicle System Interface Module is available to permit communication between aftermarket electrical accessories and the truck’s OE electrical system.

The electrical architecture itself is a version of PowerNet, the high-performance system introduced originally on the Chrysler 300, Dodge Journey, and Dodge Charger. It has one high-speed CAN (Controller Area Network) bus rated at 500 kb/s, two others rated at 125 kb/s, one of which is for telematics. Like the passenger cars, it has available the 8.4-in center-stack touchscreen.

Stiffer frame

Frames are built with 50-ksi (345-MPa) steel. The main rails are hydroformed, the rear rails are fully boxed, and there are eight crossmembers. The front frame rails are 1 in (25 mm) wider on each side, so the front springs could be moved slightly outboard as part of the three-link front suspension designed for increased roll stiffness.

The front crossmember, positioned between the front axle and engine oil pan, is a two-piece design with an extended weld surface for greater strength without the need for additional reinforcements.

The boxed rear rails are part of a structure that includes an axle crossmember with provision for fifth wheel and gooseneck hitches.

Although most HD buyers select the diesel, the 5.7-L Hemi V8 gasoline engine is the base on the 2500, and for 2013 also on the 3500 (single rear wheel) series. It is rated at 383 hp (286 kW), 400 lb·ft (542 N·m).

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