BUYERS GUIDE - HEAVY DUTY
Isuzu upgraded the N Series cab in 2015 and in late-2018, when a two-pedal, automated manual transmission model was announced.
The 2015 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 non-synchro first-gear, 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 were multi-leaf conventional types and were considerably longer and more supple than early-model Isuzu 4×4 springs.
Axles were 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 2015 NPS model range consisted 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 ranged from 2840kg to 3070kg and trailer capacity was 3500kg for all variants.
As befits a truck that’s intended to drive on very steep inclines and thereby cope with changing weight distribution, the axles and suspensions were considerably over-strength: front axle rating was 2800kg and the dual-tyred rear, a whopping 6600kg: that’s more than the entire vehicle’s GVM!
All models were built on the same 3395mm wheelbase and standard tyres were Michelin 8.5R17.5 XZT tubeless.
The 2015 models scored a restyled grille, 90-amp alternator and a freshened up interior.
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 wasn’t as easy as it was in the single cab, because the cab didn’t tilt. Instead, the crew cab had a lift-up front floor section over the engine that didn’t give anything like the same degree of access.
Also, the crew cab’s windscreen washer reservoir was under the rear floor and needed a clip-in panel to be removed. Likewise, the fuel filter was behind a little door in the rear seat compartment.
On the plus side, both cab types had 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 was a leggy 0.72:1, meaning there was not much gradeability in overdrive, so even mild freeway pulls caused 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 4×2 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: 4×2 models have the same problem, so it’s not just a case of the NPS’s firmer suspension.
Another issue with all touch screens – not just Isuzu’s – was the need for the driver to divert attention from the road. Car-style touch screens with little buttons have no place in a truck. (The 2018 screen and controls are better, but still tricky to scan and operate.)
Information screen apart, the Isuzu NPS 300 was pleasant to operate and longer springs than the originals 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 4×4 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 4×2. This configuration reduces front diff wear and noise, and saves fuel when 4×4 mode isn’t needed.
With the hubs clicked in, the dashboard rocker switch engaged 4×4 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.
The NPS 300 surprised me and also amazed a hard-to-please Rob Emmins (at the wheel in the photo 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 4×4 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 4×4 disengaged.
2018 upgrades and the AMT
In October 2018 I had the opportunity to drive Isuzu’s AMT automated manual transmission model on-highway and off-road. The truck specifications remained pretty much as with the 2015 models, but with a very important change to the proved powerplant
The 5.2-litre 4HK1 turbo-charged and air-to-air intercooled, four-cylinder, 16-valve diesel lost its fancy ‘Sitec’ description and, much more importantly, also lost its diesel particulate filter. Everyone with experience with DPFs in current diesel utes and light trucks hates the bloody things.
The NPS 300 2018 emissions kit was diesel oxidation catalyst (DOC) based, so there was no bushfire hazardous DPF that needed periodic regeneration and no need for AdBlue. Hooray!
The engine retained its 114kW at 2600rpm output and 419Nm in the 1600–2600rpm rev band.
A downside of using a relatively large capacity engine in a light truck is fuel consumption. Our on and off road testing in a loaded crew cab NPS saw average fuel consumption at 18-20L/100km.
Another addition to the 2018 specification was a change from Michelin XZT 8.5R17.5s to Bridgestone L330 225/80R17.5 tyres, giving 200kg additional front axle capacity. (They’re still way too skinny for soft ground work, however and there’s still no sign of wide single tyres as an option.)
Interior upgrades for 2018 included cruise control and a new audio-visual system, featuring 6.2-inch capacitive touch-screen with greater brightness and resolution. It ran an Android Automotive operating system for fast responses and included USB 3.0 connectivity, BluetoothV4, AM/FM/DAB+ and internet radio, when using a tethered smartphone wifi.
On and off road
I haven’t been a fan of Isuzu’s self-shifter since its introduction in 4×2 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 in 4×2 trucks has a stator in the fluid coupling and that produces torque multiplication of 1.55:1, resulting in improved response at lift-off. However, in the 2018 NPS 300 4×4 models there’s no stator and, hence, no torque multiplication: low range gearing is there for that purpose!
On road, 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.
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.
The new AMT 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.
When highway driving in high range I discovered one quirk that’s caused by the transmission’s retention of a non-synchronised first gear. The AMT was happy to upshift and downshift through the four synchronised gears, but it wouldn’t pick up first gear on the run. That was a problem only on one extremely steep gradient – estimated 15-percent – that I encountered without momentum. The box chimed a warning, indicating the need to stop and restart in first.
In demanding off-road terrain, after low-range selection, the AMT functioned as a two-pedal manual box, with gear selection being done with the stubby lever. It retained whatever gear the driver selected, so control was easy and positive, with no risk of unwanted upshifts or downshifts.
If the driver selected a gear that was too high for the traction and speed conditions the fluid coupling ‘slipped’ to compensate, but when there was too much slip the warning chime sounded, indicating it was time for a downshift.
The Isuzu NPS 300 is more refined than it used to be and the frills haven’t come at the expense of off-road ability. However, suspension quality still 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 aluminium single wheels and a Wedgetail slide-on camper.
Single cabs have a RRP of 88 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 fleets and motorhome builders.