You should know the probable effect on the engine when instrument indications vary considerably from the specified values. When variations occur in instrument indications, before taking any corrective action be sure the instruments are not at fault before you try corrective actions on the engine. Check the instruments immediately if you suspect them of being inaccurate. Periodic inspections are also important in detecting engine troubles. Such inspections will reveal the failure of visible parts, presence of smoke, or leakage of oil, fuel, or water.
Cleanliness is probably one of the greatest aids in detecting leakage.
When you secure an engine because of trouble, your procedure for repairing the casualty should follow an established pattern, if you have diagnosed the trouble. If you do not know the location of the trouble, find it. To inspect every part of an engine whenever trouble occurs would be an almost endless task. You can find the cause of the trouble much more quickly by following a systematic and logical method of inspection, Genernlly speaking, a well-trained troubleshooter can isolate the trouble by identifying it with one of the engine systems. Once you have associated the trouble with a particular system, the next step is to trace out the system until you find the cause of the trouble.