An engine operator probably relies more on the instruments to detect impending troubles than on all the other trouble symptoms combined. Regardless of the type of instruments you use, the indications are of no value if inaccuracies exist. Be sure an instrument is accurate and is operating properly. All instruments must be tested at specified intervals or whenever they are suspected of being inaccurate.

Smoke

Smoke is a useful aid for locating some types of trouble, especially if you associate smoke in conjunction with other trouble symptoms. The color of exhaust smoke can also provide you with clues in troubleshooting.

The color of engine exhaust is a good, general indication of engine performance. The exhaust of an engine that is in good condition and operating under normal load has little or no color. A dark, smoky exhaust at normal load indicates in-complete combustion; the darker the color, the greater the amount of unburned fuel in the exhaust. Incomplete combustion may be due to a number of troubles. Some manufacturers associate a particular type of trouble with the color of the exhaust. The more serious troubles are identified below:

1. Bluish-white smoke

a. Worn or stuck piston rings

b. Worn cylinder liners

c. Worn valve guides

d. Cracked pistons

e. Leaking injectors

2. Black or gray smoke

a. Incompletely burned fuel

b. High exhaust back pressure (clogged exhaust ports, piping, or muffler)

c. Restricted air inlet (clogged inlet ports, air cleaner, blower inlet screen)

d. Malfunctioning turbocharger

e. Improperly timed or faulty injectors

f. Engine overload (cylinders not balanced)

g. Low compression (burned valves or stuck piston rings)

Excessive Consumption of Lube Oil, Fuel, or Water

An operator should be aware of engine trouble whenever excessive consumption of any of these vital liquids occurs. The possible troubles indicated by excessive consumption will depend on the system in question. Leakage, however, is one trouble that may be common to all systems. Before starting any disassembly, check for a misaligned system or for leaks in the system in which any excessive consumption is occurring.