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Understanding and Profiting From the Caterpillar C7

Even in today’s struggling economy, there are still creative ways to make an income, and the same is true with the transportation industry. I am sure there are plenty of automotive and diesel engine shops finding new areas in which to direct their expertise.

By Bob McDonald

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I believe society naturally directs the outcome of its environment: if someone manages a quality independent automotive repair shop, they will always be looking for ways to increase their education and specialty tools as technology changes. In order to take care of their customers when the warranty runs out and they no longer visit the dealership, shops need to adapt.

A quality independent automotive repair facility that keeps up with technological advances is no different than any other competitive industry. Look at the automotive manufacturers themselves. Today’s society has directed them to make more power, use less fuel and offer more features.

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The Cat C7 was available with the following horsepower ratings:
210, 230, 250, 275, 300, 330, 350 and 360 hp.

Torque ratings ranged from 520 up to 925 lb-ft. The 201, 230 and 250 hp. ratings were available in either a low torque or high torque option.

The choice of torque options allowed different transmissions, which are rated by torque capacity, to be matched with the C7. The 330 through 360 horsepower ratings were only available in RV and firetruck
applications.

The same can be said about the heavy-duty industry as well. Heavy-duty diesels that transport goods across the country along with the ones that are used to excavate highways are all using the same competitive strategies to stay on top. In addition, the EPA has raised standards and lowered emissions in response to or as a cause of technological advances.

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The Caterpillar C7 engine is no exception. Another popular Cat engine, they’re now seeing rebuilding opportunities, so we thought we would take a look at how things have changed to get to where we are today.

From 2003 to 2009, the C7 was Caterpillar’s primary engine for medium-duty trucks with a GVWR of 18,000 to 33,000 lbs. from GMC, Ford, Freightliner and Paccar. The Cat C7 is an inline 6-cylinder diesel engine with a displacement of 7.2 liters or 441 cubic inches.

At the end of its production cycle, the engine included a number of features including turbocharging, common rail fuel injection system, full electronic control system and Caterpillar’s ACERT fuel/air management system. To meet regulations, advanced emission solutions include a closed crankcase breather and a diesel particulate filter using Cat’s proprietary regeneration system.

Of course, to understand where we are, it’s often necessary to take a look back. The C7 was Caterpillar’s answer to growing demands for emissions reductions and was derived from its older engine brother, the Cat 3126.

The 3126 was, in fact, the replacement for the Cat 3116 and that’s where this story REALLY starts. The 3116 engine was used up until the mid ’90s until society demanded more. The 3116 caused strong reactions in many people, to say the least. Not too many 3116 owners were proud of Cat’s reputation behind the engine and, while the engine did prove reliable, it didn’t offer enough power for most users and was not very fuel-efficient.

To counter its poor reputation and meet tightening emissions demands, Cat released the 3126 in 1997 as its first midrange electronic diesel engine. The 3126 could be found in GMC, Ford and Freightliner trucks, Thomas and other school buses, recreational vehicles and smaller emergency vehicles. It was also offered in off-road applications as well in excavators, skidders, motor graders, industrial, and marine.

Depending on application, the 3126 ranged from 175 to 300 hp. It was a part of the “gear fast, run slow” strategy from Cat, which allows the engine to run slower at cruise speeds, translating into potential reduced fuel consumption. The 300 horsepower version produced peak power at 2,200 rpm with the torque peaking at 800 ft.lbs. at 1440 rpm.

To achieve its electronic advancement the 3126 engine utilized HEUI (Hydraulic Electronic Unit Injector). All HEUI designs work in the same fashion. The components include an ECU (Electronic Control Unit), electronic injectors, and various sensors placed on the engine and vehicle. This same technology is also found in the Ford Power Stroke and was used by International in several different applications with their inline six-cylinder engines in the DT series trucks, but HEUI is a trademark of Caterpillar.

Caterpillar used high-pressure oil to make even higher injection pressures, effectively squeezing fuel out of the injector nozzle. In a HEUI system, the oil pump inside the engine supplies oil to a high-pressure oil pump or HPOP.

The HPOP is gear-driven by the engine and sends pressurized oil to a galley in the cylinder head that surrounds the injector.When the ECU commands the injector to open, the high-pressure oil enters the injector and pushes down on an intensifier piston inside the injector body which in turn pushes down on a plunger.

The intensifier piston is generally seven times greater in size than the plunger. At idle, the HPOP supplies approximately 500 psi of pressure to the injector. Caterpillar used high pressure oil to squeeze fuel out of the injector nozzle. The injector has two compartments in the lower portion of the injectors body. One for high pressure oil to enter the injector and the other is to store incoming fuel which is provided by a pump at 80 psi.

When the injector is commanded to open, the 500 psi oil enters and then sends fuel out of the tip at 3,500 psi (7 x 500 because of the intensifier piston). At wide open throttle, the HPOP can supply the injector with up to 3,000 psi of oil pressure. So, the fuel being ejected from the injector tip can reach as high as 21,000 psi.

The volume of oil that is supplied by the HPOP is controlled by an electronic regulator. The various sensors monitor HPOP pressure in relation to engine parameters from coolant temperature, oil temperature, cam position sensor, throttle position, manifold pressure, and barometric pressure. Utilizing these electronic controls along with high-pressure oil brought about more precise engine control as well as more economy. This engine design also increased power and reduced emissions.

One thing that really set the 3126 apart was the design of its cylinder head. The inline-six cylinder head incorporated three valves per cylinder: one exhaust valve and two intake valves. The head was named “cross-flow” and revolutionized the airflow of the engine. Incoming air entered the engine from the right hand side through the intake valves and exited through the exhaust valve on the left hand side.

This cross-flow design changed the swirl characteristics of the cylinder head and was a big factor in improving power and combustion on this diesel engine. With all of these changes in the 3126, the power was almost double that of the 3116.