Kenworth K108 truck review

By: Tim Giles

Kenworth’s flagship, the K104, is now the K108. Tim Giles takes it out on the highway to see what’s changed

Kenworth K108 truck review
Kenworth K108.


There is a simple answer to the question about what is different in the new Kenworth K108 — very little. On the surface, and from a driver’s point of view, this is true.

However, delve a little deeper and there is a lot more going on beneath the surface to ensure little has changed for the driver.

Another situation remaining unchanged will be Kenworth’s dominance of the heavy duty truck market and the K108’s dominance within that range.

This is the industry-standard cab over prime mover and, as long as the brand is held in such high regard by Australian drivers, should remain so.

Kenworth reckons 10,000 K Series have been sold in Australia and New Zealand since 1971. The basis of its success lies in two distinct areas.

One is the straight-forward Aussie design. Kenworth keeps on coming up with no-nonsense, simple engineering solutions to the kind of battering trucks get running at 100km/h on our roads.

The ad hoc nature of the design means each individual component can be improved without needing a rethink on the whole truck. This is true from engines and chassis members all the way to switches on the dash.

The second is in the brand image of Kenworth.

The K108, like the K104 before it, pushes the buttons of truck drivers with plenty of chrome and stainless steel. Interiors with buttoned leather and woodgrain dashes are still the go.

Plus, of course, the choice of Cummins and Caterpillar engines giving out a swift torque rise and the right-sounding growl coupled with the faithful 18-speed Roadranger.

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The advent of ADR 80/02 did present some major issues for Kenworth’s Chief Engineer Gary Hartley and his team. Unlike many of its competitors, Kenworth did all of the development work locally. No other market in the world had to shoehorn the new engines and cooling packages into the K series envelope.

The new engines use exhaust gas recirculation (EGR) or ACERT technology and throw out considerably more heat than their predecessors. This means a much bigger cooling package taking up a lot more of the cab over’s limited frontal area.

Another major issue, about which little was heard, was the new ADR 83, introduced at the same time. This calls for an extensive rethink of noise reduction equipment fitted around the engine and muffler.

Radiator size was solved by raising the cab 80mm on its mountings, giving room for the larger equipment and improving air flow around the engine.

Sound deadening presented a much more difficult problem calling for a more complex solution using materials to absorb sound rather than simply shield and encapsulate the engine compartment causing airflow issues.

The K108 as tested by Owner//Driver is the classic B-double spec we can expect to see on our roads in 2008.

Fitted with a 2.3-metre Aerodyne sleeper on a 4,280mm wheelbase, the prime mover can be fitted with a bullbar and haul a 34-pallet B-double set while still fitting inside the 26-metre B-double envelope.

The Dana D46-170 rear axles are rated at 20.9 tonnes, while rear suspension is Kenworth’s own Airglide 460.

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The engine is a 625hp (466kW) Caterpillar C15 Acert putting out 2,050ft lb (2,779Nm) of torque.


This drives through an 18-speed Autoshift using the Cobra shift control.

Cab and Controls

First impressions suggest there is nothing new and it is only when parked side by side at a truckstop with a K104B that the differences become clear.

The cab does sit a little higher but it is not obvious from the driver’s seat, although the 2.3-metre cab does make a difference to the feeling of space inside the cab.

Visibility in the K Series is an issue when comparing the truck with many of its competitors but Kenworth has made the best with what it has.

The small window in the passenger door is fitted with a mirror giving a good low-level view on the nearside of the truck. The stepped windows in both doors have improved visibility on both sides since their introduction a few years ago.

The repositioning of the door introduced with the K104B last year does improve the view of the rear view mirrors and there is no need to stoop to see the whole mirror.

The large engine hump in the middle of the K108 cab squeezes space as it always has done in K Series models. While seating and steering wheel position are good, there is limited room to move for larger drivers.

Even for this driver the need to set the seat forward to get a comfortable position for the right foot on the accelerator brings the clutch a little too close to the left leg when cruising in top gear.

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The instrument layout remains similar to the K104 and everything is near to hand, but the need to cram ever more equipment and information into a limited space does make for some awkward placing of controls. The air-conditioning is positioned low down beside the steering column and can be difficult to see and control.

The seat fitted in the test truck is not to this driver’s taste as it allows too much forward and back rocking motion when travelling at speed.

The Isri option would be preferable for this driver but many drivers seem to like the looser setting of the KAB seat.


The route Owner//Driver used for the test took in a couple of legs on a three-day road trip from Coffs Harbour in New South Wales to Mildura in Victoria calling in at Newcastle, Wagga and Swan Hill on the way.

This gives an opportunity to sample inter-capital highway driving and some of the lower grade two-lane experience further west.

Fully loaded over 60 tonnes, the K108 pulling a tautliner set was part of one of two cavalcades criss-crossing the country bringing the new Kenworth range to the trucking public.

Unfortunately, for this test the truck is a pre-production prototype and as a result it is impossible to gauge information like fuel consumption.

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The test truck is running on 4.33:1 axle ratios whereas in reality the ratio to get the most out of the new engines will be 4.11:1 or even 3.99:1 if the application the truck is intended for can handle such a tall differential.

Both the new Cummins Signature with EGR and this Cat using Acert have been designed to run at lower revs than their predecessors. Running at 100km/h a driver of the new engines can expect to glance down at the tachometer and see it reading below 1,450rpm.

Eaton has been involved in development work for the new engines and has come up with profiles for the Autoshift gearbox. There are separate settings to suit the torque and power characteristics of the C15 Acert and Cummins ISX.

On the profile for the Cat in the test truck the box chooses to upshift before the revs reach 1,600 in normal conditions and downshift as revs pass 1,300. If the driver wants to intervene in the process, the policy of now fitting the Cobra shift lever is an improvement on some of the earlier controls used in Kenworths.

The drive was also a good chance to see how effective this cooling package actually is. The new C15 is known to reject something like 25 per cent more heat placing greater demands on the cooling system.

Although there were no long hard climbs on the route taken the fan should be expected, on the Pacific Highway from Coffs to Newcastle at 60-plus tonnes, to come into play.

But it was difficult to get the fan to kick in at all and only after some experimental gear changes at the foot of a climb left the truck to haul itself up the grade at 20km/h did the familiar roar of the Horton fan start up.

The increased size of the cooling package means an increase in fan capacity and the 11-blade fan does make quite a lot of noise. Luckily, the drive-by-noise rules of ADR 83 do not require the cooling fan to be engaged during the test.

The other familiar sound on a K series, the engine brake, is considerably quieter than on older models and even driving through wooded areas with the window down it did not sound at all intrusive — unlike those of trucks coming in the other direction whose jake brake drowned out the new Cat brake from several hundred metres away.

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Any nitpicking about driving position and space should be seen in the context of the experience of the whole truck. This is a Kenworth, a K108, the most popular heavy truck in Australia. Driving a B-double down the highway hauled by the K108 is a great experience. This truck does the simple things very, very well.

The driver gets a feeling of security from the truck and there is plenty under the right foot to keep them happy. Feedback from the truck testifies to the power available and its ability to handle the task with ease.

All Australian truck drivers know what to expect from a cab-over Kenworth and they can be reassured they will continue to get the same service from the new K108.

Doubts about the suitability of this design, originating in the ’70s, in future product plans remain. The evolutionary nature of the development of the K100 series of models means this is still a modern truck.

However, the new developments due to hit Australia in the next five years, both from regulator and buyer demands, are unlikely to be accommodated on the K100 platform. A rubber band can only be stretched so far.

This test does seem to allay the fears associated with the new engines about how easy it is to cool a big low-emission engine in a small space.

Going on the evidence so far the K108 and its engine remain cool!



Make/Model: Kenworth K108

Engine: 625hp (466kW) Caterpillar C15 Acert putting out 2,050ft lb (2779Nm) of torque

Transmission: 18-speed Autoshift using the Cobra shift control

Wheelbase: 4,280mm

Cab: 2.3-metre Aerodyne sleeper

Rear axles: Dana D46-170 rated at 20.9 tonnes

Rear suspension: Airglide 460

Capacity: Can haul a 34-pallet B-double set inside the 26-metre B-double envelope


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