Buying a used Cat-brand truck

When we checked through the used Cat Trucks entries in trucksales classifieds in August 2021 we found five used prime movers there, with varying mileages. All of them were substantially cheaper than more popular brands that had similar powertrains, so they could be very good buys.

We were impressed with the first Cat Truck models we drove back in 2010, so here’s a brief recap of our factory tour and road testing.

Cat Trucks didn’t try to be everything to everyone in the early stage in the new marque’s development. Mechanical specification variations were quite limited; wheelbases were for prime mover or rigid applications and there were no vocational variants on offer.

Single-rail chassis, taper-leaf front springs and Hendrickson HAS460 or Primaax rear suspensions were available, with Meritor 46-160 drive tandems that were good for a B-Double rating on the CT610 and 90-tonnes on-highway B-Triple, or A-double-road-train rating, on the CT630.

Standard cab appointments were high and included rear cab wall extenders, dual suspension seats, leather-wrapped steering wheel with cruise control buttons, power windows, front and side sun visors, spotter mirrors and overhead storage bins. A nice touch was the use of membrane door switches, so the power window controls wouldn’t be drowned by a rain shower, should the door be left open.

Polished aluminium wheels were standard and aero roof kits and sleeper cabs were optional.

There was considerable delay in the Cat Truck launch in Australia and the rumour mill said that indicated problems with the vehicles’ design and assembly procedures, but the quality control and attention to detail I witnessed at the Tullamarine (Melbourne) factory in 2010 were first class.

The trucks were assembled on a rolling production line, with the axles and suspensions installed on upside-down frames. Final chassis bolt torquing was done only after laser alignment of frames and axles. Multi-purpose brackets up front carried the taper-leaf spring leading bushes and mounted low-height radiator intercooler and air conditioner.

Locally-designed front under-run protection was also incorporated.

Frames with axles ran twice through the chassis-paint spray booth: once upside down and the second time right way up, so there were no paint ‘shadows’. The chassis paint finish was better than that on the cab panels of some American-factory trucks.

I was particularly impressed by the cab quality, which was top-shelf. Cat Trucks Australia used a ‘blemish sticker’ system to mark any minor faults on the trucks as they made their way through the production process. Major faults, such as scratched plastic mouldings or rubs on aluminium or chrome in shipped components didn’t make it anywhere near the production line. I inspected some rejected components and was amazed at the tiny degree of damage it took for a component to be rejected.

But the proof of the pudding, as they say, is in the eating. My test drives were in two of the several ‘test mules’ that Cat Trucks had been evaluating during 2009-10. They were pre-production units, but didn’t look it, other than for a sectioned dashboard with visible wires, which made for easy test-instrument fitment.

I did a pre-trip check with ease, thanks to a bonnet that tilted with little effort. I was particularly interested in the right hand drive steering layout, given the relative bulk of the Cat ACERT series-turbocharging plumbing.

From a layout point of view the steering could have been designed for RHD, because there was no tricky shaft routing necessary. A flexible mounting bush was evident, as was a coated spline section to absorb the relative movement between chassis and steering wheel.

Getting in and out of the CTs could hardly have been easier, via staircase-layout tank steps, complete with punched-out ‘grip holes’ and well-positioned grab handles in the cab doorway. Clambering onto the chassis decking was also easy, thanks to hefty grab handles fitted to the cab extender panels.

These pre-production trucks had been given a hard time, in the hands of many different drivers and somewhere along the way an overzealous left foot had fried the CT610’s clutch brake and, on top of that, the clutch was in need of some adjustment. That made gear selection a little tricky, but the rest of the Eaton RTLO 18918B transmission package was in good shape.

This short-cab truck featured a huge back window, which did nothing for sound deadening, so there was exhaust stack feedback into the cab – not noisy, but noticeable. Linehaul trucks with sleepers would be much quieter, I reckoned.

It’s hard to beat an Eaton that has a stick going straight into the box and both truck's shift actions were positive, with easy-to-feel gates.

At just under 40 tonnes GCM the CT610’s combination of 470hp and 1650lb ft (2240Nm) made light work of pushing the combination along at legal speeds. This truck was geared for short-haul work and revved to 1550rpm at 100km/h. The more powerful CT630 was completely unfazed by 40 tonnes GCM and had a 3.9:1 gearset that dropped cruising revs to under 1500rpm. That’s normal today, but was novel, back in 2010.

What the written engine specs couldn’t convey was the flexible grunt that kicked in from as low as 1000rpm, meaning very little gear changing in traffic. With two turbos stuffing air into both engines they could burn more fuel at lower revs, giving the driver rewarding response to prods on the loud pedal. We’re used to that these days, with common-rail injection and variable-vane turbos, but back then it was class-leading.

Our track headed north-west out of Melbourne on secondary roads, littered with short, sharp inclines and dozens of roundabouts. I got to swap quite a few cogs and check out each three-stage Jake Brake that proved very powerful from as low as 1400rpm. The Jakes were also quiet, growling rather than ‘rattling’.

The test route took in plenty of broken, rutted bitumen and I was impressed with the taut feeling of these pre-production trucks: not a squeak; not a rattle. The steering was kick-free and accurate, with good road feel and not too much hydraulic assistance.

The combination of taper-leaf front springs and air-suspended HAS 460 rear end worked well, producing a comfortable ride with flat handling through the twisty bits. Bendix ABS four-channel braking was powerful and judder-free and the system also incorporated electronic traction control as a standard fitment.

The failed Cat Trucks initiative cast an underserved shadow over the CT610 and CT630 that didn’t suit every customer and every application, but were fine for the mainstream of short-haul, intrastate and linehaul business.

Many cab and chassis parts are common to the later International products.

The principal problems I’ve heard of with Cat ACERT engines relate to the US-market DPFs that we didn’t need here. Also, some owners have baulked at the cost of replacing two turbos at rebuild time, but there are several single-turbo replacement kits available from the USA, at prices varying from around $US4500 to $US8000.

Cat’s mission was to avoid the complex emissions control kit that modern trucks have today. In the USA they’d been making ACERT (Advanced Combustion Emissions Reduction Technology) engines for some time, but to meet stricter 2007 US emissions rules they’d had to fit DPFs (diesel particulate filters). What we didn’t know in Australia was that these DPF-equipped ACERT engines were having issues.

Cat’s Melbourne HQ was keen to avoid that, so they built at least a year’s stock – without DPFs – ahead of Australia’s similar ADR80/03 compliance deadline of December 31, 2010 and all these trucks were 2010-plated.

So, how did Cat manage to meet ADR80/02 emissions with exhaust gas recirculation or exhaust gas after-treatment by way of DPFs or selective catalytic reduction (SCR)?
Caterpillar’s ACERT engines used series turbocharging, with Miller-Cycle valve actuation and exhaust oxidation catalysts.

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ACERT used series-turbo pairing, with a high-pressure turbo and a low-pressure turbo. The smaller, high-pressure turbo was fed exhaust gas first and then the flow went to the low-pressure turbo. That was radical then, but is commonplace on small diesel engines today.

At the ACERT introduction in 2002 in the USA that I attended, there was no mention of the Miller-Cycle concept. Only when competitors published the fact did Cat acknowledge its use of the Miller principle that’s common in some of today’s car engines.

A Miller-Cycle engine leaves the intake valve open during part of the compression stroke, so that the engine is compressing against the pressure of a supercharger or turbocharger, rather than the internal pressure of the cylinder.

The compression stroke is two discrete cycles: the initial portion when the intake valve is open and final portion when the intake valve is closed. As the piston initially moves upwards in what is traditionally the compression stroke, the charge is being pushed back out the still-open valve.

Typically this loss of charge air would result in a loss of power. However, in the Miller-Cycle, the piston is over-fed with charge air, so pushing some of the charge air back out into the intake manifold is entirely planned.

The effect can be increased efficiency, at a level of about 15 percent, because the piston gets the same resulting compression as it would in a standard engine, but with far less work. However, that’s the case only when turbocharging can compress the charge using less energy than the pistons would use to do the same work.

Variable inlet-valve timing ensures that the Miller-Cycle function can be tuned or even switched off to suit engine revs and load.

Caterpillar chose a path that involved generating excess combustion air to control the formation of nitrogen oxides (NOx). Most other makers reduce the amount of oxygen in their combustion chambers by recirculating exhaust gas into the cylinders (EGR), to achieve the desirable low-temperature combustion that produces low NOx.

Caterpillar’s approach made surplus air available and combined that factor with variable inlet valve timing, so that the compressed air temperature inside the cylinder was at a level that resulted in low-NOx combustion.

ACERT imposed loads similar to those encountered with EGR engines, because water jacketing was necessary on the output from the second turbo, to drop air temperature before the flow entered the intercooler. This subsidiary cooling requirement meant that the larger radiators being used for EGR engines were also necessary for ACERT engines.

Caterpillar holds several US Patents on the variable valve timing system it employed in the ACERT program. In principle the system isn’t far removed from the familiar Jake Brake actuation, where oil is used to actuate exhaust valves, rather than mechanical lift from the camshaft.