An MO21 pilot notices that the oil temperature was slowly rising over several days of flying and whi...

Attributes
ACN	382431
Time
Date	199710
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : dxr
State Reference	CT
Altitude	msl bound lower : 3500 msl bound upper : 3500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : dxr
Operator	general aviation : personal
Make Model Name	M-20 E Super 21
Operating Under FAR Part	Part 91
Flight Phase	cruise other
Flight Plan	None
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : private
Experience	flight time last 90 days : 27 flight time total : 550 flight time type : 270
ASRS Report	382431
Person 2
Affiliation	Other
Function	other personnel other
Qualification	other other : other
Events
Anomaly	aircraft equipment problem : less severe other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

After takeoff and cruise climb to 3500 ft I noticed that the oil temperature was somewhat higher than usual after level off. It was reading about 200 degrees F and that was about 30 degrees hotter than usual, but still in green. I decided to return to dxr and check it out on the ground. I called dxr tower and explained I had a somewhat high oil temperature and requested priority (but did not declare emergency, since all temperatures were still in green). I landed, did extensive run- up and temperatures stayed in green. I took off again without incident. The oil temperatures stayed in mid-green at cruise and I returned and landed without incident. I felt fairly sure that the earlier high temperature observation had been erroneous on my part, an error due to my parallax view of the gauge or something. A flight on the following day, oct/sat/97, was also fine, with all temperatures in the mid- green. But on oct/sun/97, I flew again and noticed that the oil temperature gauge was showing higher than usual oil temperatures and leaned over to make sure that the reading was above normal (the reading was around 200 degrees to 210 degrees F). I immediately returned to danbury airport, keeping a close eye on the gauges (the oil temperature gauge never left the high area of green, but was clearly 30 degrees higher than normal, all other indications were normal and mid-green (cht, egt, oil pressure). On oct/mon/97, I called my mechanic and asked him to check it out. He found a failing vernatherm valve to be the culprit. I have learned from this experience that it pays to be very cautious regarding 'clues' the airplane gives regarding impending failures, and if something doesn't seem quite right, assume the worst and get it checked out immediately. All of the above flts were in VFR conditions. I can only imagine the potentially catastrophic problems that could have been encountered if I had launched into low IMC without having had the bad vernatherm valve diagnosed and replaced.

Original NASA ASRS Text

Title: AN MO21 PLT NOTICES THAT THE OIL TEMP WAS SLOWLY RISING OVER SEVERAL DAYS OF FLYING AND WHILE IT WAS STILL WITHIN THE LIMITS HE DECIDED TO HAVE THE SYS CHKED BY A MECH. THE MECH FOUND THAT THE OIL TEMP CTL VALVE WAS MALFUNCTIONING.

Narrative: AFTER TKOF AND CRUISE CLB TO 3500 FT I NOTICED THAT THE OIL TEMP WAS SOMEWHAT HIGHER THAN USUAL AFTER LEVEL OFF. IT WAS READING ABOUT 200 DEGS F AND THAT WAS ABOUT 30 DEGS HOTTER THAN USUAL, BUT STILL IN GREEN. I DECIDED TO RETURN TO DXR AND CHK IT OUT ON THE GND. I CALLED DXR TWR AND EXPLAINED I HAD A SOMEWHAT HIGH OIL TEMP AND REQUESTED PRIORITY (BUT DID NOT DECLARE EMER, SINCE ALL TEMPS WERE STILL IN GREEN). I LANDED, DID EXTENSIVE RUN- UP AND TEMPS STAYED IN GREEN. I TOOK OFF AGAIN WITHOUT INCIDENT. THE OIL TEMPS STAYED IN MID-GREEN AT CRUISE AND I RETURNED AND LANDED WITHOUT INCIDENT. I FELT FAIRLY SURE THAT THE EARLIER HIGH TEMP OBSERVATION HAD BEEN ERRONEOUS ON MY PART, AN ERROR DUE TO MY PARALLAX VIEW OF THE GAUGE OR SOMETHING. A FLT ON THE FOLLOWING DAY, OCT/SAT/97, WAS ALSO FINE, WITH ALL TEMPS IN THE MID- GREEN. BUT ON OCT/SUN/97, I FLEW AGAIN AND NOTICED THAT THE OIL TEMP GAUGE WAS SHOWING HIGHER THAN USUAL OIL TEMPS AND LEANED OVER TO MAKE SURE THAT THE READING WAS ABOVE NORMAL (THE READING WAS AROUND 200 DEGS TO 210 DEGS F). I IMMEDIATELY RETURNED TO DANBURY ARPT, KEEPING A CLOSE EYE ON THE GAUGES (THE OIL TEMP GAUGE NEVER LEFT THE HIGH AREA OF GREEN, BUT WAS CLRLY 30 DEGS HIGHER THAN NORMAL, ALL OTHER INDICATIONS WERE NORMAL AND MID-GREEN (CHT, EGT, OIL PRESSURE). ON OCT/MON/97, I CALLED MY MECH AND ASKED HIM TO CHK IT OUT. HE FOUND A FAILING VERNATHERM VALVE TO BE THE CULPRIT. I HAVE LEARNED FROM THIS EXPERIENCE THAT IT PAYS TO BE VERY CAUTIOUS REGARDING 'CLUES' THE AIRPLANE GIVES REGARDING IMPENDING FAILURES, AND IF SOMETHING DOESN'T SEEM QUITE RIGHT, ASSUME THE WORST AND GET IT CHKED OUT IMMEDIATELY. ALL OF THE ABOVE FLTS WERE IN VFR CONDITIONS. I CAN ONLY IMAGINE THE POTENTIALLY CATASTROPHIC PROBS THAT COULD HAVE BEEN ENCOUNTERED IF I HAD LAUNCHED INTO LOW IMC WITHOUT HAVING HAD THE BAD VERNATHERM VALVE DIAGNOSED AND REPLACED.

Data retrieved from NASA's ASRS site as of July 2007 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.

An MO21 pilot notices that the oil temperature was slowly rising over several days of flying and while it was still within the limits he decided to have the system checked by a mechanic. The mechanic found that the oil temperature control valve was malfunctioning.