by Bob McDonald
The engine came standard with a turbo made by Garrett. At first, the engine was turbocharged without an intercooler. If you look on the turbo outlet of the compressor side of the turbo you can see that a “Y” pipe is connected to direct air from the turbo into the intake manifold. The reason for no intercooler was the size of the turbo.
In 1999, Ford introduced an intercooler for the same 7.3 DIT engine. The intercooler was put into production on the Ford trucks because there was a change in the turbo. The compressor wheel was larger and the change to a bigger turbo brought more boost and higher exhaust gas temperatures. The new turbo was capable of maximum boost of 28 psi, which needed to be controlled.
Garrett installed a wastegate, mounted in the turbine side of the turbo. There is a wastegate actuator mounted on the compressor side of the turbo, connected to the wastegate by a rod. So when the compressor housing makes boost beyond what is needed, the actuator opens the wastegate.
In 2003, Ford introduced the 6.0 DIT engine for its Diesel trucks with a turbo known as variable geometric turbo (VGT) made by Garrett for this engine.
As engine speed rises, the powertrain control module (PCM) commands a solenoid to open at a desired rate to change the geometry of the “vanes” in the turbine housing. This is used to operate from no boost at idle to full boost at wide open throttle (WOT).
Before the Power Stroke, Diesels were generally defined as indirect injection (IDI) engines. When the Power Stroke was introduced by the International Corporation new terminology came into use: direct injection (DI). Direct injection is used on the 7.3- and 6.0-liter engines. The use of computer control and direct injection made for less emissions and more power, bringing Ford’s Diesel engines into the modern age.
With DI, Diesel fuel is pressurized electronically at the injector of the cylinder that is being fired. Other manufacturers were using electronic systems for Diesel injection, but they were also using an external pump to pressurize the Diesel fuel. The International Corporation used engine oil under high pressure along with various sensors and lines to make Diesel fuel pressure at the injectors.
7.3 Fuel Supply
Fuel is stored in the tank and must be pressure-fed to the fuel injectors. On the 7.3 from 1994 to 1997, fuel came from the tank through fuel lines to a mechanical engine-driven pump, which is located in the central valley of the engine behind the turbocharger.
One side of the pump is the inlet, used to suction fuel from the tank and deliver it to the fuel filter basket. The fuel pressure coming into the fuel filter basket is anywhere from 3 to 7 psi. On the other side, at the fuel filter basket is a water separator drain.
When entering the second stage, fuel is compressed further and sent to the cylinder-head–mounted fuel injectors at 40 psi.
6.0 Fuel Supply
The 6.0 fuel system is very similar to that on the later 7.3. This system has an electric pump known as a horizontal fuel conditioning module (HFCM). The HFCM is frame-mounted, and is controlled by the engine’s computer. The condensation drain (water separator) is integrated into the pump, as is a serviceable pre-filter.
The Power Stroke oiling system is not radically different than that of other internal combustion engines. The only major design differences are the high-pressure path required
by the high-pressure oil pump (HPOP) and the oil cooler.
There are differences in the HPOP systems of the 7.3 and 6.0. Even though their functions are similar, the differences are worth noting. There are two system types: the low-pressure system and the high-pressure system.
7.3 Low-Pressure System
The oil pump in the 7.3 engine is of a “gerotor” design. As the crankshaft spins, the gear on the front turns the rotor (vane) inside the oil pump. Oil is drawn through the pick-up screen mounted in the oil pan.
When oil reaches the pump it is then pressurized and sent through the front cover. The front cover has two passages by which the oil enters the block. One passage leads to the reservoir for the HPOP. The other passage sends oil to the oil cooler, which is mounted on the side of the engine.
7.3 High-Pressure System
In order for the oil to enter the HPOP reservoir, it must pass through a check-ball assembly integrated into the front of the block. During cold starts, the HPOP receives unfiltered oil through the check-ball passage until reaching a nominal operating temperature.
When oil enters the HPOP, it is pressurized and sent through hoses that run to both cylinder heads.
Oil then travels through the high-pressure passages to surround each injector. When the injector is fired, the oil drives the internal piston down inside the injector body. After the piston in the injector is driven down and the piston returns to the top the oil is “spit” out of the injector through an orifice mounted on the side of the top of the injector.
The oil then drains back through holes leading to the oil pan.
6.0 High-Pressure System
The 6.0 HPOP is housed in the rear of the motor. The crankshaft, camshaft, and HPOP are gear driven from the rear of the engine. The front of the engine has no gears other than the crankshaft, which turns the engine oil supply gerotor pump.
As the HPOP spins from the rear geartrain, it pressurizes oil received from the reservoir. The pressurized oil exits the HPOP into a pump discharge line.
The design of HPOP system in the 6.0 DI is more efficient than that in the 7.3 DI. If any leaks occur in the system they are contained by the crankcase.
If a leak occurres on a 7.3, it can be detrimental. If the high-pressure hoses come apart oil can spray everywhere, cause engine damage, and make a huge mess. The design of the 6.0 system came about by problems faced with the 7.3. The HPOP system on the 6.0 is more of a task to service, but most of the time it’s trouble-free.
This is the HPOP on the 6.0 Power Stroke. It is located at the rear of the engine underneath the turbo. The injection pressure regulator is located at the top right of the cover.
The cooling system of the Power Stroke engine does employ one component you may not be familiar with: the degas bottle. This small tank is mounted separately from the radiator and serves as the service point for the cooling system. The service cap is mounted on the degas bottle, as it is mounted higher than the radiator (which has no cap).
In general, the cooling system of the 7.3 engine is reliable. Even in the event of adding aftermarket products (such as programmers and upgraded turbos), the coolant system has proven itself to be efficient. Typical wear parts (such as water pumps and thermostats) are to be expected, but it’s rare to experience a head gasket repair or oil cooler failure.
6.0 Engine Cooling System
The 6.0 engine utilizes many of the same components as the 7.3 engine.
One thing that you need to address is the exhaust gas recirculation (EGR) cooler. In 2004, EGR valves became mandatory. The EGR systems did pose a problem when this engine was introduced. From 2004 to 2006, Navistar had some serious complaints with the EGR systems on the 6.0 engines. Additionally, head gaskets became a problem and plagued the 6.0 engine. Blown head gaskets were overheating engines and destroying them.
One head gasket problem was the material, but there are only four bolts per cylinder to secure them (compared to the six bolts per cylinder of the 7.3). Hard use over extended periods placed serious pressure on the head gaskets.
There are two solutions for the problematic EGR cooler. One is to totally eliminate the EGR from the engine. Keep in mind that this is for off-road use only. If you remove this for highway use, it is not emissions compliant.
The second solution is to replace the EGR cooler. Bulletproof Diesel sells a stainless-steel EGR cooler with a more rigid design, which offers more strength and cooling efficiency. Using this product is a great option instead of having to replace the factory cooler, and it carries a lifetime warranty.
Notice the difference between the 6.0 cylinder head (left) and the 7.3 cylinder head (right). There are four valves per cylinder versus two valves, but size does matter. The 6.0 DIT has 79 fewer cubic inches. That is almost a cylinder and a half less than the 7.3 DIT. To keep up with emissions demands, smaller packages were introduced.
In the 7.3 cylinder head, you have one intake valve and one exhaust valve. They both are the same size, 1.68 inch diameter. From 1994 until 2002, the 7.3 cylinder head remained the same. The injectors and glow plugs are under the valve cover.
When the 6.0 was released in 2003, many changes had taken place, including the cylinder heads. This was the first head from Navistar with four valves per cylinder (two intake valves and two exhaust valves). Valves measure at 1.33 and the exhaust valves measure 1.10 inches in diameter.
The cylinder head took on a totally new configuration to help meet the emissions standards. To increase port swirl, the valves were positioned in a twisted configuration in relation to the cylinder. The Diesel engine is dependent upon port swirl and with this valve layout, the combustion process is more refined and efficient.
Glow plugs from the 6.0 now have removable sleeves. On the 7.3 engine, the glow plugs thread into the top of the cylinder head in a “cast” boss leading to the combustion chamber.
As for the 6.0 engine, the glow plugs are sealed by a stainless-steel sleeve. The sleeve seals off the injector and the combustion chamber from coolant.
Because the 6.0 cylinder head has four valves per cylinder, two intake valves have to be opened at the same time along with two exhaust valves. The rocker arms are different from the 7.3 in relation to design and length. Also, the rocker arms incorporate a bridge linking the two.
Something else to note is the injector hold-downs. On the 7.3 engine the injector has a hold-down that is on the injector body. There are two bolts positioned from top to bottom where the injector sits in the cylinder head. The top bolt is installed into the cylinder head and tightened to its specific torque specification. Then the injector is installed into the cylinder head and the hold-down is positioned over the bolt already installed. Once it is in position the other bolt can be installed.
As for the 6.0, the injector hold-down is much easier to deal with. The hold-down is shaped like a horseshoe and is removable from the injector body. One caution: take care when installing the injector in the 7.3 or 6.0. Make sure to grease the O-rings on the injector along with the injectors cup in the cylinder head. Then install the injector and press it into the head by hand or with a soft rubber hammer. Do not strike the injector with a blunt object because this can damage the injector.
The rocker arms on the 6.0 DIT are attached to the rocker carrier. This is a complete assembly with all rocker arms that attach it to the cylinder head. It is held in place with Torx-head bolts attaching to the cylinder head.