Caterpillar C15 ACERT engine Buying Used Review

Alice Springs airport was unusually quiet for a Sunday afternoon. Only a smattering of baggage rode the carousel, and even the taxi rank was free. Off to a good start, at least.

'The Alice', as the locals call it, is home to G&S Transport. According to the email that arrived a few days before, the Red Centre city was the kickoff point to check out a Caterpillar ACERT engine that's been toiling with triples along the infamous Tanami Road and Stuart Highway for the most of its life.

Early next morning, Alice Springs was alive with the bustle of the new week and not far out of town at a nearby quarry; a wheel loader was busily loading roadbase into three of G&S Transport's end-tippers.

The loader's scales indicated the total load to be approximately 80 tonne, which gave the entire road train a GCM of around 130 tonne. Indeed, this would give the Caterpillar ACERT something serious to get its teeth into on the test run.

G&S Transport owner John Bilato took the wheel first and guided the Kenworth T904 out to the Tanami Road. The mainstay of their fleet comprises heavy-duty Kenworth models, and this T904 was similarly spec’d.

Under the hood is the Caterpillar C15 ACERT engine, with an Eaton 18-speed transmission and Dana D52-190 axles on the Kenworth’s big six rear end, with a final drive ratio of 4.56:1. The chassis is full-length double rails and it came equipped with all the trimmings, including full rear axle locks and pressurized bell housing.

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But first, what is ACERT? It was the technology and hardware that Caterpillar developed to take its on-highway engines to the next level. Denoting ‘Advanced Combustion Emissions Reduction Technology’, ACERT is not only one thing, but rather a combination of things that, when combined, deliver the power and reliability that transport operators expect from their Caterpillar engines.

Compared to the ever-popular C15, 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 C15 engines, and they need to be too. Turbo boost pressure has increased to an average of 42psi via twin turbochargers connected in series.

Another critical component is the variable inlet valve actuation controlled by the engine’s ECM (Electronic Control Module). It allows the inlet valve to remain open longer than in a traditional engine, thereby increasing air volume in the cylinders.

Another key to reducing NOx is maintaining lower cylinder temperatures. This is achieved by way of multiple injections, which is controlled by an additional 'bump'. In fact, this is a very tiny lobe on the camshaft that triggers the burn process before the main combustion takes place. The engine's ECM controls the primary injection delivery, which takes into account engine load and speed.

The upshot to the increased cylinder air volume and new integrated Cat Brake is that the engine braking capability has risen to 600 horsepower.

Not far down the Tanami Road, John Bilato pulled into a parking bay.

"Right-O, it's your turn to drive," John said with a smile. "There is a long pull not too far away; I'd like you to pay particular attention to how the engine handles it and let me know your thoughts.

"I find if you use bog cog to get it rolling, then take it up to around 1600rpm and shift a full gear, it’s a lot easier on the driveline. Do this till you get into sixth gear, then you can split the rest of the gears going up."

A few moments later, the tacho needle reached 1600rpm, then dropped and rose steadily again and again as the CAT ACERT-powered Kenworth gathered momentum.

An interesting point to note is Caterpillar recommends driving this style of engine at far lower revs than the older models. "In fact, it is imperative that you don't drive over 1600rpm to get the best out of these engines," John added.

It quickly became apparent that the C15 ACERT certainly didn't lack any punch, and you'd expect it wouldn't either. It is rated at 625hp and thumps out 2050lb-ft of torque. It was more than willing to respond to each command of the throttle, even from as low down as 1250rpm. It simply marched away.

The turbo-boost pressure needle wound itself around to the end of the gauge as the throttle went down and the twin turbochargers spun up, and they are nowhere as noisy as the single turbo of earlier the C15 or C16 models.

Most interesting was to note the pyrometer, which sat happily around the 400-degree mark for most of the trip. To fully appreciate this reading's significance, let's compare apples with apples. The pyrometer on earlier C15 engines would climb to around 550-600 degrees on a long pull and often sit at the start of the yellow band for the entire trip.

As the miles rolled by and the bonnet of the T904 pushed ever onwards into the vast inland desert, John explained that the fuel economy of this old Cat-powered T904 compared to other trucks he’s driven was for the most part within a few litres of each other.

"We did notice that in the wet, the ACERT engine was noticeably better on fuel," John said. "When it gets wet out here, the road surface is like glue. It just sucks the trucks down.

"There's something else too – reliability. Without question, that is arguably one of the most important considerations in our business. We don't have the luxury of 1 800 call-outs or service centres every 100 kilometres in our operation.

"Breakdowns out here are costly, and they are made up of the recovery cost to retrieve the stricken vehicle, the added cost of re-scheduling the freight, and then there's the downtime and associated cost of the repair. With Caterpillar engines, we enjoyed the reliability, and that is what we look for along with the engine's performance and economy. And it’s why it is worth rebuilding a CAT engine.

"Drivers are too hard to get as well," John continued. "Well, good drivers, I mean. If your equipment is not reliable, then you won't keep the good drivers or your clients.”

"Must be getting close to this big pull you had spoken of earlier," I said.

"We passed that about 20 kays back," John said. "This engine certainly pulls pretty well, doesn't it!"

Another feather in the ACERT engine's cap is the extended oil drain intervals. Because the engine is running so much cleaner, CAT extended the drain intervals to 15,500 litres of fuel used on mineral oil. A typical triple road train application where the engine is burning around one litre of diesel per kilometre can mean a few extra trips between service intervals.

Like all good things, they come to an end far too quickly, and the promise of a thick juicy steak and cold beer at Tilmouth Wells roadhouse was a better option than dodging kangaroos and camels in the desert darkness.

Around the table, the conversation understandably revolved around the day's drive. The ride and handling of the Kenworth T904 got full marks as to its appointments, but more on the anatomy of a T904 in another story. Today it's all about Caterpillar's ACERT engine, and why it’s still a popular choice with transport operators.

John summed up the engine neatly. “The bottom line with the Cat ACERT engine is its tenacious power output,” he said. “But, above all, this Caterpillar engine is reliable, and parts are readily available.”

One significant advantage the Caterpillar C15 ACERT engine has over engines using SCR technology is that it does not require the addition of additives to meet earlier emission requirements, which means that there is no sacrificing fuel capacity or the added expense of purchasing the additives like AdBlue.

However, given the fact that Caterpillar ceased on-highway engine production a decade ago, most ACERT engines will have had at least one engine rebuild by now, if not two. So be prepared to do your due diligence on the engine's service history.

The good news is that parts for Caterpillar engines are easily obtained.

You’d expect to pay between $105,000 to $130,000 for used Cat-powered T904, like the one in this review. However, bear in mind these units rarely come up for sale. And when they do, they’re immediately snapped up. Conversely, you’d expect to pay $95,000 to $120,000 for Cat-powered cabover Kenworth.

Budget-conscious buyers can certainly find a Caterpillar-powered bargain too – Freightliner and Western Star trucks are a little cheaper, ranging from around $55,000 to $85,000.

The good news is that regardless of which brand or model you decide on, the running gear is essentially the same and parts are readily available. Cabin wise, parts availability for older Western Star and Freightliner models, such as switches and dash trim, are starting to get a little harder to source.

There is of course a smattering of Cat-branded trucks running around, and there are a number of used units listed for sale. While the Cat engine under the hood is this vehicle’s greatest asset, there is very limited to no support for cabin components.

For my money, if I spotted a cheap Cat CT610 or CT630, I’d keep the engine and sell the rest for parts – but that’s only my opinion!

Make: Kenworth
Model: T904
Engine: Caterpillar C15 ACERT
Horsepower: 625hp (466kW)
Torque: 2050lb-ft (2779Nm) at 1100rpm
Gearbox: Eaton Fuller RTLO22918B
Front axle: Meritor MFS73 7.3T
Front suspension: 7.2t multi-leaf
Rear axles: Dana D52-190, DCDL to both axles
Rear axle ratio: 4.56:1
Rear suspension: Kenworth six-rod
Interior: Parchment trim with HD diamond
Seats: Black leather ISRI 6860/870, air suspended
Air dryer: Chicago Rawhide Turbo 2000
Bumper: Polished bullbar