Chapter 13 Exhaust Systems 303 Copyright Goodheart-Willcox Co., Inc. A coolant-type CAC (as well as the rest of the cooling system) must be kept clear of sludge, scale, and rust. These deposits can be loosened by the use of an approved cooling system cleaner. For specific instructions on CAC maintenance, refer to the engine service manual. Exhaust Pyrometers Exhaust pyrometers measure the temperature of the exhaust gases in each cylinder. The pyrometer’s gauge is generally located in the dash or instrument panel, Figure 13-39. As the pyrometer is switched from one cylinder to another, the exhaust temperature should be about the same for each cylinder. If the temperature does not fluctuate, the engine is operating normally. However, the exhaust temperature will not be uniform when the load is not balanced among the cylinders, the valves and piston rings are not tight, the nozzles are in poor condition, or other defects are present. Therefore, an exhaust pyrometer helps the operator keep the engine in good condition and properly adjusted. Careful observation of the exhaust pyrometer can prevent serious damage to the turbocharger and to the rest of the engine. Exhaust Brakes An exhaust brake is another item that is found in some exhaust systems. Like other engine brakes and retarding devices, it assists the service brakes on diesel-powered vehicles. Remember that an exhaust engine brake is used to only slow down a vehicle, not to stop it. It is not a sub- stitute for the vehicle’s brakes. The brakes must be used to bring the vehicle to a complete stop. Alternative Fuels The use of alternative fuels such as biodiesel, com- pressed natural gas (CNG), liquefied petroleum gas (LPG), liquefied natural gas (LNG), methanol, and ethanol is becoming increasingly important as a way of controlling diesel emissions. These alternative fuels produce fewer particulates and can be run lean. This means having a better chance of meeting future carbon monoxide, NMHC, and NOx standards. Ambient Charged air Cooled charged air Turbocharger exhaust Figure 13-38. Many turbocharged engines use air-to-air charge air cooler systems. (Mack Trucks, Inc.) 800 700 600 500 400 300 200 20 30 40 50 60 Percent full load 4-stroke cycle 2-stroke cycle 70 80 90 100 100 Exhaust temperature, °F Figure 13-39. The exhaust pyrometer measures the exhaust gas temperature. This measurement can be used when diagnosing emissions and performance problems. (Banks Power John Deere)