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A History and Overview of the Trucking Industry Part 7

An occasional problem that could cause a rise in engine temperature is an old or worn out hose. They can collapse internally causing a restriction that is not visible from the outside. When this has occurred, the careful driver will notice the engine temperature rising by periodically glancing at the temperature gauge on his dashboard.

A diesel engine cooling system also needs supplemental cooling additives (SCA’s). This is typically a nitrite-based additive that provides a coating around the cylinders of wet liner heavy-duty engines. SCA’s can be added to the system as a liquid or can be incorporated into the coolant filters that are located on the engines. When the SCA is added to the cooling system through these filters, it is usually a slow release filter that will gradually add the SCA to the system in order to maintain a certain balance. Test kits are available to monitor the concentration of SCA’s in order to keep the proper balance in the cooling system. They also contain chemicals that protect the system from corrosion.

The coolant circulating device of the system is the water pump. It may be driven by a belt from the engine’s drive pulleys or may be gear driven off the front of the engine. It has a suction port, the impeller and the discharge port. Coolant at a low temperature enters the suction port directly from the radiator. After it enters the pump, it is pressurized by the spinning impeller, forced out of the discharge port and then flows into the diesel engine cooling channels from the bottom upward.

The thermostat’s job is to control the coolant flow throughout the system based on its temperature. When the engine is hot, the thermostat opens and coolant flow goes from the engine to the radiator where it can be air-cooled and returned to the engine. When the engine is cold, the thermostat closes and it is diverted through the recirculating bypass which will return the coolant to the water pump and maintain a constant flow through the engine block and not go through the radiator.

The cooling system also contains a filter that helps keep the coolant clean of particulate matter, acts as a corrosion inhibitor and conditions the engine coolant. Zinc chromate is added to the coolant as it passes through the filter. The zinc magnesium plates protect engine metals from electrolytes destroying it.

In Figure 00-00 you can see that the coolant also flows to the oil cooler to maintain the oil at the proper temperature. The temperature of the air compressor is also properly maintained by the engine coolant. Coolant systems in gas engines have similar components as diesels.

Air Intake and Exhaust System

Every internal combustion engine requires the intake of air for combustion and the exhaust of the combustion’s byproducts. Atmospheric air is pulled through the air filter, into the turbocharger, the intercooler and the air intake port passages, past the intake valves and into the cylinder chambers. After compression, the exhaust valve will open and expel the gases through the exhaust port passages through the exhaust manifold and the exhaust side of the turbocharger, out of the exhaust pipe and muffler and up the stack into the atmosphere.

Air begins to enter the engine via one of three types of air inlet configurations: the bonnet, the snorkel or the canister as shown in Figure 00-00. Newer tractors have air canisters located underneath the hood to reduce wind resistance and increase fuel economy. Once through these inlets, the air will be cleaned by going through either an oil bath (wet) or disposable cartridge (dry) air filter. Oil bath filters are pretty much obsolete on newer equipment, but may still be seen on older equipment; some are located under the hood and some are outside of the cab. Disposable cartridges are the most common and require the least amount of maintenance. Under normal operating procedures/conditions, the oil bath cleaner should be cleaned every 5,000 miles. More frequent cleaning may be necessary during exceptionally dusty operation.

Disposable cartridge air cleaners operate efficiently when the engine is either idling or at highway seed. Oil bath cleaners only operate efficiently when the engine is turning over fast enough to draw enough air into the cleaner housing and keep plenty of oil splashing over the filtering elements. Idling a truck with an air bath cleaner for long periods of time would not be a good idea, especially during dusty conditions.

Most trucks are equipped with an air filter restriction gauge in order to assist the driver and fleet mechanics with proper maintenance. It is either mounted on the dash or on the air cleaner housing. The gauge will read the pressure drop across the air filter element due to the presence of dirt restricting air flow. The air filter is typically replaced when the pressure drop reaches 25° of H20.

A turbocharger is very efficient and places minimal demand on the engine while at the same time giving an additional horsepower boost. A turbocharger is a fan-like piece of equipment that takes the increase in pressure from the exhaust gases to spin a turbine which is connected by a shaft to another turbine, which is taking in air from the air filter, compressing it and forcing it into the cylinders under pressure.

The operation of the turbocharger is contingent upon the volume of exhaust gas. The higher the engine RPM, the more air pressure the turbocharger can produce. It is an ideal design and functions well in higher altitudes.

A temperature-measuring device installed to monitor the temperature of exhaust gases is termed a pyrometer. It allows the driver to watch the temperature of the turbocharger to prevent damage from excess heat.

A normal operating temperature is obtained during highway driving when the pyrometer shows a temperature range between 600° to 1100°. Typically, the maximum safe reading is 200° below the engine’s maximum operating temperature although the safe temperature range may vary depending on the tractor. Driving in mountainous, steep terrain or long gradual upgrades seem to present the most danger of overheating the turbocharger. Once the air leaves the turbocharger it is pressurized. The air is directed through intake system piping to a charge air cooler. This unit is mounted directly in front of the radiator and looks similar to a radiator. The charge air cooler reduces the temperature of the compressed air significantly before it enters the intake manifold and cylinders. The cooler air helps lower air temperatures, resulting in greater horsepower capability from the engine. The engine also becomes more efficient which results in better fuel economy and lower emissions.

The air is further routed to the intake manifold via more piping. Once the fuel-air mixture is ignited by the compression in the cylinders, the exhaust is then discharged past the exhaust ports and into the exhaust manifold. If the exhaust gases were put directly into the atmosphere, the noise would be deafening. Mufflers are used to quiet the noise created by exhaust gases. According to federal regulations, exhaust systems on trucks have to have total decibel readings that do not exceed 80 decibels at 50 feet.

Mufflers are designed to minimize the noise of exiting hot exhaust gases, but not so much that it constricts the flow of the gases. If the gases were constricted, it would cause back-pressure at the engine and reduce engine performance. Most mufflers are constructed with a series of perforated pipes and baffles that allow some of the energy to be dissipated. Mufflers redirect the exhaust gases through a series of small openings, thus reducing noise.

One type of popular muffler configuration is a vertical muffler and vertical outlet, which moves the exhaust from the turbocharger outlet, under the cab’s floor, up one corner of the truck and through a single muffler into the atmosphere.

Another type of configuration is the horizontal muffler and horizontal outlet which hangs a muffler and outlet pipe on the frame. This is otherwise known as a framemount and releases the gases close to the pavement level.

A third configuration is a horizontal muffler and vertical outlet where the muffler hangs on the frame, but the outlet pipe winds upward. Some buyers desire this configuration for aesthetic rather than functional reasons.

Gasoline Engines

Diesel engines are always used in heavy trucks, but gasoline engines are oftentimes used in light to medium-sized trucks (typically less than 33,000 gross vehicle weight) and buses. Gasoline and diesel engines both perform the same function by creating the torque and horsepower to move a vehicle.

Like a diesel engine, a gasoline engine also includes fuel, lubrication, cooling and intake/exhaust systems. Most of these systems are very similar, but the main differences are between the compression and combustion part of the engine’s cycle.

Gasoline engines used in trucks are four-stroke. Figure 00-00 shows how a gasoline engine compresses fuel and air as opposed to only air a diesel engine. Fuel is injected in the intake manifold prior to going through the inlet port into the cylinder. The timing of this is controlled by computer, and varies depending on the engine design.

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