REVIEW: Kenworth MX-13 engine

By: Matt Wood, Photography by: Matt Wood

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After previewing the Kenworth MX-13 engine prototypes last year, Matt Wood takes the officially launched MX powered T409 range for a drive.

Since the end of 2010 Cummins has been the sole choice of engine for the Kenworth brand until the introduction of its very own MX range.

Kenworth buyers now have the option of the traditional red engine or the silver in-house power plant. When I say ‘its own engine’ I mean the Paccar MX has come to the Kenworth stable from the other Paccar brand DAF.

The engine itself is nothing new and 1,000 units have been sold in Australia since 2007 in the DAF brand.

The Australian launch of the DAF flagship, the XF105, two years ago certainly raised the profile of the MX-13 and no doubt paved the way somewhat for wider acceptance of the engine.



The MX-13 is a 13-litre engine using selective catalytic reduction (SCR) for emissions control. It’s available in two different power ratings; 460hp (343kW) and 1,700ft-lb (2,300Nm), or 510hp (380kW) and 1,850ft-lb (2,500Nm).

The MX is being launched on a platform of lightweight, driveability and economy. The MX uses a compacted graphite iron (CGI) block that makes it very light (about 1,200kg) very strong and surprisingly quiet.

CGI is becoming quite popular as the material of choice in high performance car engines as well and is often used for exotic European V configuration engines.

The MX-13 is also sold in the United States and has been offered as an engine option in both Kenworth and Peterbilt products. The Aussie Kenworth MX however is based on the Dutch-built Euro spec MX though it does share some castings with the American version.

These castings are to help the 13-litre nestle between the chassis rails of a conventional prime mover rather than the European cab-over configuration of the DAF product.

With mandated fuel economy regulations on the way for Class 8 (heavy-duty) prime movers there could be even more take up on the way for the little silver engine.

The addition of the MX engine to the Kenworth line-up now means for the first time a 24-volt truck will be rolling off the Bayswater assembly line. Past experience with the DAF XF105 and the MX engine has indeed backed up the fuel economy claims

Behind the MX there’s the option of the time honoured Eaton manual or the two-pedal Eaton UltraShift automated manual transmission (AMT).

Apart from the diesel exhaust fluid (DEF) tank and the distinctive shape of the exhaust after-treatment box hanging from the chassis, there’s little else to distinguish the MX powered T4 from a Cummins powered rig.

I got the chance to take the production spec finished products for a spin at the Australian Automotive Research Centre (AARC) near Anglesea in Victoria.

The assembled rigs are set up in both single trailer and B-double guise and weights are up from the last Queensland drive to between 35 tonne and 62 tonne gross.

The vehicles include the T409 and the T409 SAR, and for good effect the DAF product is also well represented.



My first spin is in an UltraShift AMT equipped B-double.

Programming an AMT to take orders from a different engine is no small task. The MX has a typically European torque curve that gives peak torque from 1,000 to 1,400rpm and peak horsepower from 1,500rpm to 1,900rpm.

The 16-speed ZF AMT used in the DAF performs admirably behind the MX, and I am dubious about how the 18-speed Eaton in this particular model will perform behind the MX. As it turns out I am pleasantly surprised.

While I don’t have the chance to drive it bob-tail or to hook up and drop trailers with it, which is generally a big area of weakness with the Eaton ‘box, I do get to play with it at low speed forward and backwards.

The ceramic clutch of the Eaton, while durable and cost effective has made it hard to get slippage in delicate low speed situations.

The MX’s high pressure common-rail fuel injection gives impressive fuel delivery control at low rpm and there’s now some slippage possible in the clutch making it much more controllable at low speed.

Going forward at normal road speeds the AMT behaves beautifully making the most of the low down torque in bottom box and skip shifting where possible. At higher speeds the AMT and MX wind out higher in the rev range picking up some of the 13-litre’s oomph.

The marriage of the UltraShift plus AMT and MX-13 engine is by far the best performing Eaton AMT application I’ve driven to date.

Next up is the Kenworth T409SAR B-double with an old school manual shifter in it.

I know from past experience the MX is quite torquey and very forgiving on the gear changing front. But with a bit of extra pudding on its back I am still impressed with its performance.

A short shuffle through bottom ‘box is easily done before making the jump up to high range and interestingly in top ‘box the engine is happy to change whole gears on flat ground, even at this weight.

I am basically driving it as a 9-speed progressively upshifting and leaving the splitter button alone. With each gear change the tacho needle drops and the engine digs in shouldering the load and lugging it along with impressive tenacity.

At one stage on a climb, against all instincts, I let the silver donk lug down to 850rpm and to my surprise it actually claws its way back up the rev range, without needing me to grab a lower ratio.

Like many of its Euro competitors’, peak compression braking horsepower is up at around 2,000rpm. To get the most out of it a pre-emptive drop out of overdrive at highway speeds is required, rather than relying on the initial grab of a Cummins/Jake brake combo.



The MX-13 stacks up nicely in a part of the market that is starting to look crowded with 13-litre product.

It lugs along and feels nicely balanced and at home under the T4 bonnet shroud. However, Kenworth buyers still have the option of a 15-litre Cummins in the T4 with horsepower ratings up to 600 galloping gee gees.

This installation is perfect for bulk tipper and dog and single trailer applications where light tare weight and axle weights have a dollar value. Diminishing load B-double, 19m B-double or light double applications that top out at between 50 tonnes and 55 tonnes also play to the MX’s strengths.

It’s a very driveable engine with surprising performance for its displacement. But, at this stage there’s no substitute for cubic inches and Australia remains largely a 15-litre market so for the time being the red 15-litre especially in e5 form is most likely going to remain the donk of choice for heavier B-double and line-haul applications for the T4.



Engine: 12.9-litre Paccar MX-13 with high pressure common-rail fuel injection.

Construction: CGI

Emissions Control: SCR

Power: 460hp (343kW) @ 1,400 to 1,900rpm or 510hp (380kW) @ 1,500 to 1,900rpm

Torque: MX-13 460 — 1,700ft-lb (2,300Nm) MX-13 510 — 1,850ft-lb (2,500Nm)

GCM: 70,000kg


For the full report, grab a copy of NewFarmMachinery magazine issue 11, on-sale July 14. Subscribe to the magazine to never miss an issue. 


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1 Kenworth T409 truck Looks the same, sounds completely different. 1 Kenworth T409 truck
2 Kenworth MX13 single trailer work Single trailer work is a walk in the park for the MX. 2 Kenworth MX13 single trailer work
3 Eaton UltraShift Plus The Eaton UltraShift Plus and I don’t have a great history, but in this case it’s a very nice installation. 3 Eaton UltraShift Plus
4 Kenworth MX13 engine The 13-litre MX engine is constructed out of CGI for lighter weight while retaining strength. 4 Kenworth MX13 engine
5 Kenworth MX13 in Local B double At 510hp, Local B-double is a promising role for the new engine. 5 Kenworth MX13 in Local B double
6 Kenworth MX13 under the bonnet It’s a long time since I’ve seen a colour other than red under a Kenworth bonnet. 6 Kenworth MX13 under the bonnet
10 Kenworth MX13 ideal for bulk transport Bulk transport is the kind of role that the MX is ideal for, especially in the set forward steer axle SAR. Those belly dump trailers are also magic to tow. 10 Kenworth MX13 ideal for bulk transport

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