Paccar MX13 engine in Kenworth T403 and T409 review

By: Matt Wood

Kenworth has announced that the company is trialling the Paccar MX13 engine in its T403 and T409 bonneted prime movers. A sceptical Matt Wood climbs behind the wheel and is forced to rethink some old prejudices

Paccar MX13 engine in Kenworth T403 and T409 review
Paccar MX13 engine.


When Kenworth announced recently it was trialling the 13-litre Paccar MX engine in the T403 and T409 conventional, my preconceived ideas were again being challenged.

I mean, really? A Kenworth with a European DAF motor? That’s just bloody un-Strayun that is! But true it is. Kenworth has a number of MX13-powered test units on the road in varying roles at present and all the while the engineering and product development team at Bayswater are monitoring and collecting data on the new installation.

Rather than try to keep things under wraps for too long, Kenworth recently gave the media and prospective customers a chance to drive some MX-powered KW models at the Mount Cotton test facility in Queensland.

For me, the first impressions of the driveline were surprising to say the least. Great, more preconceived ideas blown to hell.


The 13-litre MX engine is available in two guises globally.

Paccar manufactures an MX engine in the United States for their domestic market. Last year, 29 percent of all Kenworth and Peterbilt trucks sold in the US had an MX engine ticking away under the hood.

In Europe, the MX is made at the DAF Eindhoven factory in the Netherlands. The Aussie MX hails from Europe, although in a heavy-duty form that includes a titanium-bladed turbo charger and an extra ‘polishing ring’ on the pistons.

The 510hp (375kW) MX is probably best known to most as the powerplant of the flagship DAF XF105. Also on offer is a 460hp (340kW) version with 1,700ft-lb (2,300Nm) of torque.

Paccar has sold 800 of these selective catalytic reduction (SCR) engines in Australia since 2007. It’s been an award winner both here and in Europe and I’ve driven the big DAF in manual and auto form, as a B-double and a single and walked away without feeling overly critical of the DAF, except for one thing … I was bored.

You can imagine that I was maybe a bit sceptical of the idea of planting a DAF donk under the fibreglass bonnet of one of Bayswater’s finest. To my mind, it had the potential to suck all of the character out of what is otherwise an engaging truck to drive.

The reasons for doing so, however, are clear; the MX is a quiet, lightweight and fuel efficient engine. And Kenworth hasn’t had an alternative to Cummins power for nearly five years, though Cummins has extended the available range to SCR engines as well.

The European pedigree of the MX is steeped in the mindset of using very tall final drive gearing and low rpm to maximise fuel economy, as a result like much of its Euro brethren the MX has a long flat torque curve.

Peak torque is available from just above idle to 1,400rpm.

Compacted graphite iron (CGI) is becoming a popular material for making high performance engine blocks both in high output exotic supercars and for heavy-duty diesel engines. The reason being is that it’s a lot lighter than a grey iron block but it’s also significantly stronger.

More is now being asked of diesel engines in terms of power output for displacement and emissions, consequently the stresses and strains on the structure of truck engines in general continues to grow. But another side effect of CGI is that it lacks the resonant qualities of a cast block, which makes it very quiet in operation.

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But in keeping with the KW theme, the Bayswater team has elected to use Eaton transmissions (above) rather than try using the ZF-AS Tronic automated ‘box found under the DAF shed.

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Just to horrify my puritanical ideas even further, these trucks are all 24-volt; the first 24V trucks to roll out of the Kenworth factory ever.

So, it was with some scepticism that I approached the line-up of glistening Kenworths and DAFs at the test track just south of Brisbane.

My fears were somewhat allayed on firing up the MX, but while behind the wheel of a T403 hooked up to a single tipper; it still sounded right. At my left hand was a familiar looking Eaton gear stick, so a slotted a cog, let the clutch out and got the ball rolling. I was surprised immediately. Taking the MX out from under that cosy, well-insulated DAF shed gave the engine note an edge that to date I hadn’t heard before.

As I worked my way up through the cogs, the yellow 403 answered the beck and call of my right foot admirably, even admitting a satisfying little sigh from the turbo waste gate as I changed gear.

The Mount Cotton circuit is quite tight and compact, with plenty of twists and turns as well as some up-hill action. As I’d found when driving the Eaton-equipped DAF some time ago, it can also take a little while and some tacho watching to tune your ear to what the engine is doing and when you should go for a gear.

The MX rewards low rpm changes that make the most of the low torque range before winding the mill out a bit more once the rig is up and rolling.

At this stage, the engine brake control for the MX is a button located on the floor just to the left of the steering column.

Most of those present agreed this was a less than ideal location for it, as it required you to either stretch your throttle foot across to reach it, or to use your clutch foot to operate it. This was counterintuitive to say the least and felt a bit like you were driving a big bendy fork lift rather than a truck.

However, it seems that this would be unlikely to make it into any production units when the time comes.

After parking the little yellow wagon, I jumped into a T409SAR with a B-double set of tippers behind it, which brought the red rig to a gross weight of 55 tonnes.

The extra weight meant that momentum was my friend when getting all of the wheels turning.

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Again, the MX surprised me with its willingness to get up and boogie, especially  with the extra kilos rolling along behind.

What’s more, the MX even got a bit of a snarl up as it had to work that bit harder.

It was kind of startling, like being bitten by a cute little doggie that you’ve known for years.

The location of the engine in the T400 range means that you’ve got no choice but to maintain an intimate relationship with what’s going on under the bonnet, as the back of the engine is just about inside the cab.

The T409’s twin hood-mounted air intakes could be heard taking great gulps of oxygen as I again put the foot down; you are left with no illusions as to what’s taking place under the bonnet at any given time.

To some this may be considered a criticism, but from my point of view, if you want to be away from the action, you’ll opt for the DAF product anyway. The rawness of the MX in the Kenworth is no more than you’ll find in any of the existing Cummins power plants.

In fact, the CGI block makes it a tad quieter, and anyone who’s spent any time behind the wheel of these trucks in their present spec will not find the noise obtrusive.

You might be tempted to say that the 510hp (375kW) MX may be a little light on for 26m B-double duties and, to be honest, I’d agree. While the engine is more than capable of handling a 62-tonne-plus load, it does tend to breathe a little heavy and work up a bit of a sweat.

But at 55 tonnes, it seemed quite happy indeed and it seemed to me that it’s no mere accident that this engine is nestled between the chassis rails of an SAR.

The performance of the lightweight donk planted it firmly in my mind as an ideal candidate for 19m B-double work as well as tipper and quad dog and the steer axle-forward configuration of the SAR has the perfect footprint for these jobs; did somebody say Performance Based Standards (PBS)?

Another nod in the direction of the MX’s low rpm operation is some of the final drive ratios that Kenworth has been playing with.

One T403 at the drive was equipped with a 3.42:1 ratio and another T409 was running a 3.7:3 ratio, very tall ratios indeed.

Again, the torquey nature of the MX came into play; the blue T403 was pulling a single trailer at around 35 tonne gross and was equipped with an Eaton Ultrashift Plus

AMT. The Eaton box spoke to the engine well and I was surprised at the low speed performance of the driveline.

Clearly, the 3.4 final drive keeps the rpm low at highway speeds. The white 409 was hooked up to a B-double set which tipped the scales in the mid-50s and also fitted with an Eaton AMT box.

This proved to be a very neat combination, the 3.7 rear end provided a good balance between the pulling power of the MX and the horsepower developed higher up the rev range.

The only really noticeable downside of the taller gearing is engine braking performance.

Like many other Euros, peak engine braking performance is higher in the rev range and the MX really grabs the road at around 1,900-2,100 rpm. The exhaust brake/hydraulic engine brake is very effective but only really with a down change.

Those used to just bleeding highway speed off with a Jake brake would find the braking performance of the system a bit lacking. But if you’re willing to drop a cog or two on a descent the MX will hold back a double quite well.

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The MX/Kenworth trial will continue until the Kenworth team is satisfied that it has tweaked the concept to the point where it’s production-ready.

The fuel efficiency and light tare weight of the MX will no doubt be an attractive proposition for some applications.

The MX13 also weighs in some 200 kilos lighter than a Cummins ISX, a healthy margin for bulk operators especially for those where steer axle weights are on a knife edge.

From behind the wheel, the 12.9-litre puts out more punch than I’d previously been prepared to give it credit for, enough for me to have to rethink my earlier position on the lightweight Euro.

And even more importantly, I wasn’t bored because, really, it is all about me after all.


Make/Model: Paccar MX13 Engine

Capacity: 12.9 litres

Construction: CGI

Power: 460hp (340kW) to 510hp (375kW)

Torque: 1,700ft-lb (2,300Nm) to 1,850ft-lb (2,500Nm)

Fuel System: High pressure SMART multi-point injection

Emissions: SCR


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