MALFUNCTION PROBABLE CAUSE CORRECTIVE ACTION For all engines Slow loss of RPM during cruise flight Carburetor or induction icing or air filter  clogging Apply carburetor heat. If dirty filter is  suspected, divert to closest airport. High cylinder head temperature (CHT) Insufficient airspeed for cooling (for ram air  cooling systems) Reduce throttle. Increase airspeed. Improper mixture adjustment Reduce throttle. Land as soon as possible. Detonation or preignition Reduce power, increase cooling airflow.  Land as soon as practical.  Very high cylinder head temperatures  (CHT) and climbing Cooling system failure Reduce throttle and land as soon as  practical. Shut off engine if readings climb  well above manufacturer’s limits to avoid  engine damage. Low cylinder head temperature (CHT)  Excessively rich mixture Reduce altitude. Extended glides without clearing engine Clear engine long enough to keep  temperatures at minimum range. High exhaust gas temperature (EGT) Lean mixture from improper jetting (can  result from jetting set for higher altitude  airport and flying to lower altitude airport) Reduce throttle. Land as soon as practical.  Lean mixture from additional air leaking  into induction system Reduce throttle. Land as soon as possible.  Low exhaust gas temperature (EGT) Rich mixture from improper jetting Land as soon as practical. Ammeter indicating discharge Magneto/generator failure Shed unnecessary electrical load. Land as  soon as practicable. Rough running engine Improper mixture Land as soon as practical.  Carburetors out of adjustment or out of  synchronization (more evident at lower  rpm) Idle at higher rpm. Land as soon as  practical. Detonation or preignition Reduce power. Land as soon as practical.  Induction air leak Reduce power. Land as soon as practical. Plugged fuel nozzle (for fuel injection) Reduce power. Land as soon as practical. For four-stroke engines only  High oil temperature Oil congealed in cooler Reduce power. Land. Preheat engine. Inadequate engine cooling Reduce power. Increase airspeed. Detonation or preignition Observe cylinder head temperatures for  high reading. Descend to enrich mixture. Forthcoming internal engine failure Land as soon as possible. Defective thermostatic oil cooler control Land as soon as possible.  Low oil temperature Engine not warmed up to operating  temperature Warm engine in prescribed manner. High oil pressure Cold oil Warm engine in prescribed manner. Possible internal plugging Reduce power. Land as soon as possible. Low oil pressure Broken pressure relief valve Land as soon as possible. Insufficient oil Land as soon as possible. Burned out bearings Land as soon as possible. Fluctuating oil pressure Low oil supply, loose oil lines, defective  pressure relief valve Land as soon as possible. Figure 13-8. Common inflight abnormal engine instrument indications, causes, and corrective inflight actions. 13-14