Usage:
3208 Truck Engines ( 40S)
Caterpillar diesel engines equipped with Exhaust Gas Recirculation (EGR) systems are available at the present time only in California for use in on-highway trucks. Since these trucks can be driven to other areas, this article gives some general information about the basic purpose, operation and maintenance of this equipment.
The EGR system is used to keep engine emissions low during normal operation. The emissions from a diesel engine are variable in relation to engine temperature, rpm and load factors. To control these emissions at acceptable levels, the EGR system causes a part of the exhaust gas to flow back through the inlet manifold to the engine cylinders where it changes the characteristics of combustion. The system automatically adjusts the amount of exhaust gas that flows back to the cylinders according to engine load, to give the desired combustion characteristics. This lowers the emissions of nitrous oxide and other gases, and causes less exhaust smoke, especially during operation of a cold engine before it warms to normal temperature.
3208 Engines equipped with the EGR system use a crankcase breather on the valve cover instead of a Positive Crankcase Ventilation (PCV) valve, and have a 3° automatic timing advance in place of the normal 5° automatic timing advance. The engine is rated at 200 BHP at 2800 RPM. Except for maintenance of the breather in place of the PCV valve, lubrication and maintenance recommendations are not changed for engines equipped with the EGR system.
The EGR system operates a valve at the outlet of the left exhaust manifold to control the amount of EGR. Only the one valve is used; there is none on the right manifold. When the system is correctly adjusted, the valve moves to either of three positions, in relation to engine load: 1) With the engine at low load, the valve is open to permit maximum EGR. 2) Between low load and full load, the valve permits approximately one-half EGR. 3) At full load, the valve is closed-no EGR.
The EGR valve on the exhaust manifold is operated by a hydraulic actuator that has two solenoid valves which are controlled by a switch on the fuel injection pump housing. The hydraulic actuator uses engine oil pressure to operate the EGR valve.
When there is any failure or other problem in the system, the EGR valve on the exhaust manifold will be held in the open position for maximum EGR. This will cause loss of power and an increase in exhaust smoke. The engine can be operated in this condition if necessary, but engine efficiency will be low, and the oil and oil filters must be changed after repairs are made to the EGR system. Make necessary repairs to the EGR system as soon as possible.
A more complete explanation of the EGR system, with details of operation, specifications and service information is given in the "Service Manual for Low Emission 3208 Engine With Exhaust Gas Recirculation--Serial Numbers 40S1-up", Form SENR7455. This form is for use in the Service Manual for 3208 Truck Engines, Form SENR7012.