Narrative:

Upon climbing out I noticed a slightly lower than normal manifold pressure on the left engine (31' vs 32' normally expected). Condition persisted through the cruise portion of flight though no other abnormal indications were observed. Upon descent from 6;000 to 4;000 feet; the indicator for 'left alternator off' illuminated. I ran the checklist; confirmed on the ammeter that the left alternator was off line; and the right was picking up the load as designed. On confirming that no circuit breakers had tripped; I attempted to recycle alternator which was unsuccessful.[later in the flight]; I glanced out my side window at the left engine and noticed a trail of smoke emanating from below the left engine nacelle. I rechecked all my engine instruments and found nothing out of the normal range. This plane also has fire annunciating system with detection loops in each engine; and there also was no annunciation of a fire condition. I decided to divert at this point and [contacted] approach informing them I had smoke coming from my left engine. They said [a suitable airport] was about 10 miles behind me and I said I would divert to there. Controller cleared me for the visual. Upon my turn back towards [the divert airport]; I noted that I was too high to perform a stabilized descent and requested a left 360 to lose some altitude. I was cleared to do this. Half way through my left 360; I noted the left oil pressure began dropping abnormally low and advised ATC that my left engine may be failing. I was re-cleared for the visual and subsequently landed without incident. Arff followed me to the ramp and once the engine was shut down; the smoke dissipated. There was no fire. Upon exiting the plane and conducting an inspection of the left engine area; I determined the smoke must have been emanating from the exhaust pipe.

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Original NASA ASRS Text

Title: Twin Cessna pilot reported diverting to a nearby alternate after experiencing left engine abnormalities.

Narrative: Upon climbing out I noticed a slightly lower than normal manifold pressure on the left engine (31' vs 32' normally expected). Condition persisted through the cruise portion of flight though no other abnormal indications were observed. Upon descent from 6;000 to 4;000 feet; the indicator for 'Left Alternator OFF' illuminated. I ran the checklist; confirmed on the ammeter that the L alternator was off line; and the R was picking up the load as designed. On confirming that no circuit breakers had tripped; I attempted to recycle alternator which was unsuccessful.[Later in the flight]; I glanced out my side window at the left engine and noticed a trail of smoke emanating from below the left engine nacelle. I rechecked all my engine instruments and found nothing out of the normal range. This plane also has fire annunciating system with detection loops in each engine; and there also was no annunciation of a fire condition. I decided to divert at this point and [contacted] Approach informing them I had smoke coming from my left engine. They said [a suitable airport] was about 10 miles behind me and I said I would divert to there. Controller cleared me for the visual. Upon my turn back towards [the divert airport]; I noted that I was too high to perform a stabilized descent and requested a left 360 to lose some altitude. I was cleared to do this. Half way through my left 360; I noted the left oil pressure began dropping abnormally low and advised ATC that my left engine may be failing. I was re-cleared for the visual and subsequently landed without incident. ARFF followed me to the ramp and once the engine was shut down; the smoke dissipated. There was no fire. Upon exiting the plane and conducting an inspection of the left engine area; I determined the smoke must have been emanating from the exhaust pipe.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.