Doosan DL420 wheeled loader Geoff Ashcroft

By: Geoff Ashcroft, Photography by: Geoff Ashcroft

Date: 10.04.2013

Five years after launching the DL400, Doosan has rolled out of a series of updates to its popular wheeled loader to create the DL420

Doosan DL420 wheeled loader

Longer torque curve at lower rpm makes it more fuel efficient
Doosan's boom suspension, Load Isolation System (LIS) makes for a comfortable ride
Easy to operate with the throttle and joystick
Extra bucket capacity now available

The five-year old DL400 was one of the original DL models that replaced the former Daewoo Mega range, but rather than give this revised version a "Mark II" badge, the Korean maker has slipped in the DL420.

The firm says that the reasoning behind the change in model number is to build on the success of the DL400 by giving its replacement a larger capacity engine, which in turn offers much more low rpm torque. This will reward operators with lower emissions and better fuel efficiency

Engineering and performance

The DL420 uses the same basic architecture, chassis, transmission, axles and loader arms as the DL400. There is a realignment of bucket capacities, up from the DL400's 3.9 cubes to 4.5 cubic metres.

Most loader pins have increased in diameter from 90-100mm, giving an increase in bearing surface area of almost 50 percent to cope with the extra loading.

The cab is largely unchanged, save for a new instrument panel and supplementary switch gear to allow deeper interrogation of what's going on inside.

Power now comes from a Cummins QSM11, as found in the larger DL450 and flagship DL500 models, which brings two more litres of engine capacity over and above the DL400's QSL9.

Engine and power

This larger Cummins motor packs a 310hp peak, which occurs at 1700rpm, with rated power falling away to 280hp at 2000rpm. Maximum torque delivery takes place at 1400rpm, where 1450Nm finds its way out of the QSM11's crankshaft, giving near identical performance to the outgoing model.

At lower rpm though, the torque curve is held up for much longer and, combined with the larger capacity engine, this has the potential to translate into a fuel saving of around 10 percent, claims the firm.

Controls

Standard specification remains high, including climate control, electrically heated mirrors, ride control and a joystick control system.

The DL420 keeps the integration of forward and reverse shuttle control on the loader's joystick control, and this is in addition to the standard steering column-mounted twist grip lever, and gives operators greater choice in how machine control is executed.

Cleverly, the transmission has three shift patterns, chosen from a rotary dial on the lower dash panel: operators can choose from manual operation, automatic shifting using gears 1-4, or automatic shifting using gears 2-4.

Selecting a maximum gear on the left-hand twist grip then gives a useful level of restraint where low speed limits are in place on sites.

The twist grip still remains the priority system for direction changes, which means the operator needs to activate the joystick buttons for shuttle operation.

There is also a kick-down function on the joystick too, giving access to first gear when climbing steep stockpiles or when you need some extra muscle when loading.

Other features of the cab include an air suspension seat and a steering column that adjusts for reach and rake, plus cab pressurisation, air filtration and climate control.

The cab is carried on viscous, so there is a generous level of vibration damping and noise suppression. Operator comfort is further enhanced with Doosan's boom suspension, called Load Isolation System (LIS).

Beneath the right-hand cab window are two hinged panels providing access to the cab filtration system. Behind the cab there are swing-out rear mudguards that help maintenance access in and around the engine and cooling compartments.

Air filter and exhaust silencer are located over the top of the engine, while the offside contains two diesel filters.

The test

The DL420's roomy cab is easy to access and features several storage areas and a cool box. The interior has black and grey plastics throughout. The air seat is fully adjustable and very comfortable too.

Switchgear is laid out in a logical pattern to the right of the operator, and all are clearly and sensibly marked.

All round vision is excellent with a low front windscreen line, well-positioned mirrors and a reversing camera.

I have a choice of transmission controls, but favour the joystick forwards/reverse thumb button control system and activate the controls that will allow me to keep my left hand on the steering wheel and my right hand on the loader joystick.

It is just so easy to use, but only after it has been activated. Doing so requires the neutral button on the front of the joystick to be pressed first, along with an authorisation button on the back of the joystick.

And this sequence of events has to be carried out every time the engine is restarted. Ok, so you soon get into the habit and I guess safety sits high on the list. This control pattern stays activated unless you press the neutral button or use the traditional shuttle lever.

I opt to preset third on the shuttle lever as my highest gear, then flicked the transmission mode selector round to "automatic gears 2-4".

My selection means first gear is only accessed using kick-down, and fourth is never brought into play, so the box should spend most of its time working in second and third - and third gear should keep revs down on load and carry, contributing to fuel savings.

Once transmission choices have been made, driving the Doosan is just a matter of pressing the throttle and toggling between forward or reverse direction arrows with your thumb on the joystick - it is that easy. And it works very well indeed, allowing quick and effortless shuttle changes, and great modulation too.

The extra bucket capacity now available on the DL420 comes in handy, and it takes little effort to fill it. A gentle prod of the throttle soon buries the bucket into the largest pile of stone now gathered under one of the screen's discharge belts.

I dab the R button with my thumb and pull the loader away from the stockpile with a secure bucketful of material. Reversing round, I cover the brakes and thumb the F button to smoothly change direction.

All that's needed is a gentle push of the throttle to ease the loader forward, and then easing off the throttle provokes an early upshift into third gear. The DL glides easily across site at low rpm.

Doosan's LIS boom suspension is working gently in the background, adding to the ride quality too.

As I approach the stockpile and ease off, the transmission glides into second - if I hadn't been looking at the dashboard, I wouldn't have felt it - I then bury the throttle as the loader starts its climb.

Nearing the crest, I raise the loader arms slightly and tip the bucket to empty the first pass onto the heap. A tap of the R button coincides with my left foot hovering over the brake pedal, and I change direction and ease the DL420 back down the ramp. Adjustable boom height control and return to dig complement the responsive loader controls, making this load and carry task an effortless one.

This loader is more than comfortable working in an envelope that spans 1200-1700rpm, and this is where operators will notice just how effortless the DL420 handles its tasks.

Operating this DL420 feels no different to the DL400 and DL350. The Korean maker has cleverly engineered a feeling of no fuss, no loudly screaming engine and no intrusive hydraulic whines into its DL line-up. This one really is a quiet machine.

The DL420 has the potential to be more fuel-efficient and remains a very competent loader.

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