SMOKESmoke can be quite useful as an aid in locating sometypes of trouble, especially if used in conjunction withother trouble symptoms.The color of exhaust smoke, a good indication ofengine performance, can also be used as a guide introubleshooting. The exhaust of an efficiently operatingengine has little or no color. A dark, smoky exhaustindicates incomplete combustion; the darker the color,the greater the amount of unburned fuel in the exhaust.Incomplete combustion may be due to a number oftroubles. Some manufacturers associate a particulartype of trouble with the color of the exhaust. The moreserious troubles are generally identified with eitherblack or bluish-white exhaust colors.NOISESINSTRUMENT INDICATIONSCONTAMINATIOFPRESSURESMOKETEMPERATURESPEEDOF LUBE OIL,FUEL, OR WATERPounding(mechanical)Knocking(detonation)Clicking(metalIic)RattlingLow lube oilLow lube oilIdling speed notBlack exhaustFuel oil in thepressuretemperaturenormalsmokelube oilHigh lube oilHigh lube oilMaximum speed Bluish-whiteWater in the lubepressuretemperaturenot normalexhaust smokeoilLow fuel oilLow coolingSmoke arisingOil or grease inpressure (inwater tempera-from crankcasethe waterlow-pressure fuel ture (fresh)Water in the fuelsupply system)oilLow coolingHigh coolingSmoke arisingAir or gas in thewater pressurewater tempera-from cylinderwater(fresh)ture (fresh)head SmokeMetal particlesfrom enginein lube oilauxiliary equipment (blowers,pumps, etc.)Low coolingLow cylinder ex-water pressurehaust temperature(salt)High coolingHigh exhaustwater pressuretemperature in(salt)one cylinderLow compres-sion pressureLow firingpressureHigh firingpressureLow scavengingair receiver pres-sure (super-charge engine)High exhaustback pressureFigure 3-43.—Symptoms of engine troubles.3-41
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