HEAVY DUTY

ISUZU NPS 300

The market-leading light 4x4 truck.

Isuzu has upgraded the N Series cab and off-road models share the changes. In mid-2018 a two-pedal, automated manual transmission model was announced.

isuzu nps 300 crew cabIt's been a few years since I tested my spine's resilience in a square-rigged Isuzu, having promised myself I wouldn't venture off the blacktop in one until the company fitted springs that actually flexed.

That was done in 2013: not to the point where the ride was plush, but it's almost acceptable for a vehicle with a high degree of off-road capability.

The upgraded cab boasted an information screen with optional navigation system and reversing camera compatibility, power windows, central locking and cornering lights.

All these additions were ideal for the NPS 300 – particularly central locking in the case of crew cab models, because in previous models it was difficult to operate the rear-seat door locks unless someone was actually sitting in the back.

The controls were modernised, with two simple rocker switches to engage four wheel drive and low range replacing yesterday’s lever.

Beneath the cab were familiar mechanicals: Sitec 155 Euro V, 5.2-litre, four-cylinder, common-rail, turbo-intercooled diesel, with cooled EGR and a DPF.  Figures were114kW at 2600rpm and 419Nm in the 1600-2600rpm band. The main box was a synchro overdrive five-speed, coupled to a two-speed transfer case.

The chassis remained an 850mm-wide flexible ladder frame that's weldable: an important feature for many off-road customers who want to add custom gear. Springs are multi-leaf conventional types and are considerably longer and more supple than early-model Isuzu 4x4 springs. Axles are live, with manually-lockable free-wheeling front hubs and a limited-slip rear diff centre. (Isuzu doesn't sell it, but there's an Eaton NoSpin automatically-locking centre available for this axle.)

The current NPS model range consists of the NPS 250 single cab, rated at 4495kg GVM; the NPS 300 single cab, rated at 4495kg or 6500kg GVM and the NPS 300 crew cab, rated at 6500kg GVM. Tare weight ranges from 2840kg  to 3070kg and trailer capacity is 3500kg for all variants.

isuzu nps 300 crew cab

As befits a truck that’s intended to drive on very steep inclines and thereby cope with changing weight distribution, the axles and suspensions are considerably over-strength: front axle rating is 2800kg and the dual-tyred rear, a whopping 6600kg: that’s more than the entire vehicle’s GVM!

All models are built on the same 3395mm wheelbase and standard tyres are Michelin 8.5R17.5 XZT tubeless.

In September 2015 the NPs scorded a restyled grille, 90-amp alternator and a freshened up interior.

In mid-2018 a two-pedal, automated-transmission option was announced.

 

On and off road

My 2015 test vehicle was an NPS 300 crew-cab tray-back, loaded to a shade over five tonnes GVM. I drove it for a day around the greater Melbourne area, on roads varying from freeway to potholed, corrugated gravel. For some serious off-road evaluation I took it to the demanding Melbourne Proving Ground, near Werribee.

Pre-trip checking the crew cab model isn’t as easy as it is in the single cab, because the cab doesn’t tilt. Instead, the crew cab has a lift-up front floor section over the engine that doesn’t give anything like the same degree of access. isuzu nps 300 crew cab

Also, the crew cab’s windscreen washer reservoir is under the rear floor and needs a clip-in panel to be removed. Likewise, the fuel filter is behind a little door in the rear seat compartment.

On the plus side, both cab types have an oil-level monitor.

The NPS 300 felt quite at home around town, with easy shifts and ample torque to mix it with traffic.

Fifth cog is a leggy 0.72:1, meaning there’s not much gradeability in overdrive, so even mild freeway pulls cause an instant speed drop. However, the NPS 300 isn’t intended to be a linehaul performer.

Vision through the windscreen and mirrors was excellent and I appreciated power main mirror adjustment as well as the wide-view spotters on both sides. Twin wipers and washers kept the screen clean.

Ergonomics were the same as in the 4x2 Isuzu N Series, so everything was well placed. My only criticism of the central display panel was the difficulty of operating it with the truck bouncing around over bumps: 4x2 models have the same problem, so it’s not just a case of the NPS’s firmer suspension.
isuzu nps 300 crew cab

Another issue with all touch screens – not just Isuzu’s - is the need for the driver to divert attention from the road. Car-style touch screens with little buttons have no place in a truck.

Information screen apart, the Isuzu NPS 300 was pleasant to operate and longer springs than the originals have made a difference to ride quality. The NPS can’t match the independently-sprung NLS for ride and handling over rough surfaces, but it’s not as bad as it used to be.

The ride compromise of having a live front axle and leaf springs is much better ground clearance and wheel travel when the going gets tough.

The going does indeed get tough at Rob Emmins’ off road facility in Melbourne’s west. This natural river-gully area has been enhanced by creation of a virtual moonscape, with steep ramps and mounds that test gradeability, articulation, ground clearance and body clearance angles to the limit.

I’ve driven 4x4 utes and wagons around this site on many occasions, but this was the first attempt in a light truck.

The NPS 300 has manually-lockable front free-wheeling hubs that disengage the front half-shafts, differential and propshaft when the truck is operating as a 4x2. This configuration reduces front diff wear and noise, and saves fuel when 4x4 mode isn’t needed.

With the hubs clicked in, the dashboard rocker switch engaged 4x4 mode instantly at any speed, provided the vehicle was running straight ahead. Low range engagement was also instant, but the vehicle needed to be stopped, or nearly so.
isuzu nps 300 crew cab

The NPS 300 surprised me and also amazed a hard-to-please Rob Emmins (at the wheel in the phoot at right) with its ability on the Proving Ground hills.

It handled a dirt 1:1.5 slope with ease and descended safely on engine braking with only mild brake application. When descending a notorious 1:1 slope it didn’t dig in its front bumper or drag its bodywork at the base of the hill.

Overall low range gearing reduction works out at 50:1, allowing the vehicle to climb steep grades without the need for a run-up or a bagful of revs and a flat torque curve ensures there’s no traction-breaking slug of torque as engine revs rise and fall.

My test vehicle was brand new, so it wasn’t surprising to find that disengagement of 4x4 mode wasn’t easy, because the unworn gears and dogs tended to bind-up with torque during our off-road driving. However, some straight-line driving, while swinging the steering wheel left and right, soon had low range and 4x4 disengaged.

Since doing this test I had the opportunity to drive Isuzu's AMT automated manual transmission on-highway. We've planned an off-road test for October 2018.

 

Two-pedal control

I haven’t been a fan of Isuzu’s self-shifter since its introduction in 4x2 N Series trucks back in 2005. The second-generation version was released in 2007 and still had less than desirable shifting habits. It was easily confused if the driver had a hesitant accelerator foot and at times didn’t seem to know what ratio to select.

I reckoned that Isuzu either had to improve its AMT or become a Toyota Group customer by buying Aisin full automatics for the N Series.

Isuzu Australia’s chief engineer of product strategy, Simon Humphries, must have thought the same:

“The new transmission has been developed after benchmark testing in Australia, with shift timing and logic designed to suit Australian driving conditions.”

The third-generation TC-AMT has a stator in the fluid coupling and that produces torque multiplication of 1.55:1, resulting in improved response at lift-off.

When driving the new transmission I noticed the the gear ratio gap between second and third gear had been reduced and a ‘kick-down’ detent had been added to the accelerator pedal action. When the driver demanded brisk acceleration and pushed the loud pedal past the detent position the engine revved faster and the transmission downshifted one or two gears instantly.

The TC-AMT also includes a car-like transmission lever with a ‘P’ position. In ‘P’ a pawl engages a large toothed gear-wheel on the transmission main shaft. The pawl and gear assembly is substantial, weighing 11kg and is claimed capable of holding a loaded N Series on a slope.

Unlike its predecessors the 2018 box didn’t ‘hunt’ for the correct ratio and I think that most drivers won’t know that it’s not a power-shift automatic, but a computer-controlled manual box.

Lift-off was particularly easy, thanks to the 1.55:1 stall ratio torque converter and hill-holding function. Second-gear starts were automatically selected, but there is a first-gear start override button, for steep-grade lift-offs.

The new calibration included a downshift program that worked very well in conjunction with the exhaust brake to wash off speed and there was no gear-selection ‘lag’ when the accelerator foot went back on the loud pedal.

The ‘kick-down’ function also worked well, giving car-like response, but the optional on-board Telematics gear showed up any such harsh acceleration or braking incidents as fuel-wasting transgressions!

 

Conclusion

The Isuzu NPS 300 is slightly more refined than it used to be, but the frills haven’t come at the expense of off-road ability. However, suspension quality definitely needs improving and a single-wheel option would be useful for those who don't need to run duals.

This photo shows an NPS fitted with All Terrain Warriors-sourced aluminium single wheels and a Wedgetail slide-on camper.

Single cabs have a RRP of 81 grand and the crew version is 10-percent more, so value for money is high, given that a posh 4WD wagon costs that much these days.

Optional two-pedal control, introduced in 2018, should prove popular with motorhome builders.


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