Kenworth K108 Used Review

Some time back, we asked Howard Shanks to dust off his log book and climb behind the wheel of a Kenworth K108 to file this report.

This story’s origins began some years back when Tully-based Brad Haack asked me if I’d seen the new C15 Cat ACERT engine and what I thought of them. I told him I’d had a run in one out on the Tanami Track in central Australia not so long back and that it had performed surprisingly well. “That’s okay then,” Brad smiled. “We just ordered one in a K108. It should arrive at the end of September.”

September finally came, and it was no shock that most folks up north were keen to see the new K108 when it arrived and it certainly looked impressive hooked up to the B-double too.

My phone rang a little after smoko the following Wednesday. It was Brad Haack. “What are you doing on Friday,” he casually asked. “Probably driving for you,” I replied. And, sure enough, that’s what he’d had in mind.

At the time, their K108 was doing a weekly run from Tully in the far north of Queensland, 3000 odd kilometres to the markets in Melbourne with produce grown in North Queensland.

Then it returned to Tully via Brisbane. It is a gruelling task. And companies can only perform with the aid of several drivers. The intricate system of ‘stage coach’ drivers along the route ensures the wheels of this K108 keep rolling day and night.

They refer to each driver by the section of the run they drive. So, for instance, the Tully-based driver is the ‘top-end’, the southern driver is the ‘bottom-end’ and so on. This weekend I was to be the ‘top-end’ driver.

For those familiar with the legendary Kenworth cabover, the K108 heralded a raft of noticeable changes from the previous models. Firstly, and most apparent, is the raised cabin height and the high visibility LED front signal with a taller radiator grille surround.

The design of the K108 cab access system introduced the first incarnation of wide, evenly spaced steps that extended lower to the ground than the previous model.

These new steps were complimented with an additional foot-well and new grab rails. This cab access system was developed following the recommendations of independent ergonomic OH & S specialists and designed around industry standard dimensional criteria.

These criteria included having consistent step dimensions and allowing the driver to maintain continuous three points of contact with the cab grab rails and steps system.

The steps also featured durable aluminium non-slip surfaces and LED illumination within the cab foot-wells. These LED step lights are integrated with the remote-control central locking system to automatically illuminate the cab access steps when the cab is unlocked.

This system helped safe night-time entry and exit from the cab. At the time, many industry stalwarts argued that Kenworth could have done even more to enhance cabin access on the K108.

Thankfully, many of their concerns got addressed when the K200 rolled onto the scene. Nevertheless, the K108 cabin access significantly improved compared to the K104.

Pre-trip engine oil inspections can be performed more easily on the new K108 via a bright finish stainless steel access door covering the filler tube and dipstick. The coolant header tank location remained the same, up the front behind the bug lift-up flap.

Interior cabin appointments were luxuriously for the time, and the instrument layout features the light warning cluster within the same dash location and easy-to-read prestige gauges.

Many long-time Kenworth users will notice an additional set of warning lights in the cluster in these models. In addition, the new higher door and roof afford even greater driver comfort and safety. Vision from the driver’s seat improved further with the introduction of the higher K108 cabin.

The wheelbase for standard B-Double configurations is also longer with 330mm added, allowing for twin 750-litre fuel tanks, the industry-leading fuel capacity for a 26-metre B-Double.

The spec sheet does allow for either short or longer wheelbases to suit individual customer requirements. Out the road, that extra 330mm does makes the K108 a good-handling truck.

Yet it was how the K108 performed on the road in the heat of Far North Queensland that we’d come to experience. This particular K108 derives power from the twin-turbo Cat ACERT coupled to an Eaton 18-speed transmission.

CAT’s high-torque low-revving ACERT engine introduced the world to the term ‘gear-fast run slow’ in an effort to promote the fuel economy gains from the latest incarnation of their C15 engine. Sadly for CAT engine lovers, this was to be the Caterpillar’s last production road-going engine release.

The Eaton final drive on this K108 is somewhat taller than you’d expect to find on a B-Double unit at a 3.9:1 ratio was indeed a tall ratio for the time and this application.

It quickly became apparent that the new C15 ACERT certainly didn’t lack any punch, and you’d expect it wouldn’t either. It is rated at 550 horsepower and thumps out 1850 lb-ft of torque.

It was more than willing to respond to each command of the throttle, even from as low down as 1250rpm. It literally marched away. The turbo-boost pressure gauge wound around to the end as the throttle went down and the twin turbochargers spun up. Interestingly they are nowhere as noisy as the single turbo of the earlier C-15 or C-16 models.

From a seat-of-the-pants point of view, it is interesting to note that even though there is plenty of power getting to the ground, it can be somewhat deceptive when you’re behind the wheel.

Back at the launch of the K108, we asked Ian Loy, (former) OEM account manager – Caterpillar of Australia what is an ACERT? “It is the technology and hardware that Caterpillar has developed to take their engines to the next level,” Ian explained.

“It is not just one thing, but a combination of things which deliver the power and reliability that customers expect from their Caterpillar engines.”

For starters, the C15 ACERT engine has an increased displacement from 14.6 to 15.2 litres by way of a longer stroke crankshaft. The main bearing journals are a four-bolt design instead of the two-bolt design on the earlier C-15 engines, and they need to be too. Turbo boost pressure has increased to an average of 42 PSI via twin turbochargers connected in series.

Another critical component is the variable inlet valve actuation, controlled by the engine’s ECM (electronic control module) and allows the inlet valve to remain open for a more prolonged period than in a traditional engine, thereby increasing the volume of air in the cylinders.

Another key to reducing NOx is maintaining lower cylinder temperatures. This action is achieved through multiple injections, controlled by an additional ‘bump’, in actual fact a very tiny lobe, on the camshaft that triggers the burn process before the main combustion takes place. The main injection delivery is controlled by the engine’s ECM, which takes into account engine load and speed.

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The upshot of the increased cylinder air volume and new integrated Cat Brake is that the engine braking capability has risen to 600 horsepower. In practice, the Cat Brake certainly does have the goods, as it more than adequately held the fully loaded B-Double on the decent down the Cardwell Range

The interesting point is that compared to the old C-15 550 Cat, which we indeed had praised and admired in the past, the ACERT engine brake is considerably more effective.

When Caterpillar stepped away from the on-highway market, the Haack’s, like many other truck operators, were despondent, primarily because they’d had such terrific reliability from the CAT-powered Kenworth trucks.

As a used truck, most K108s will have racked up a considerable number of kilometres, and it shouldn’t be a shock to learn that many would have wound their speedo around at least twice. Regardless of whether they are CAT or Cummins powered, most would have had a major rebuild at least once.

Even though the K108 is an older model, one in reasonable condition would be a practical local workhorse. Meantime the inclusion of the sleeper is advantageous if you need to do the old overnight run.

Additionally, spare parts availability is not an issue with this model as most components, including cabin and dash items, are still used in production trucks today.

Specifications:
Truck: Kenworth k108
Engine: Cat ACERT
Power: 550hp (410kW) at 1500rpm
Torque: 1850lb/ft (2508Nm) at 1000rpm
Gearbox: Eaton RTLO20918B, 18-speed
Clutch: Eaton 2250lb/ft Easy Pedal Advantage
Front axle: Meritor MFS 7.3t
Front susp: Multi leaf 7.5t
Rear axles: DS462-P
Rear axle ratio: 3.90:1
Rear susp: Kenworth Air-glide 200
Main driveline: Meritor RPL25
Inter-axle driveline: Meritor RPL20
Electrics: Power distribution box under sleeper
Brakes: Bendix ABS with traction control
Fuel: Alloy tanks, 2 x 750lt
Wheels: 10-Stud Alloy

Here are a few used K108s from our classified ads (correct at the time of writing).
2010 Kenworth K108 $97.000
2010 Kenworth K108 $140,000
2010 Kenworth K108 (110 rated with hydraulics) $110,000
2009 Kenworth K108 Big Cab $170,000
2009 Kenworth K108 $129,900
2008 Kenworth K108 $99,999