RECIPROCATING ENG GETS HIGH OIL TEMP AND LOW OIL PRESSURE WHEN FLOWN AT ALT DURING COLD TEMP WX (MINUS 20 DEGS C).

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DURING FLT AT CRUISE ALT; I NOTICED A LOWERING OF OIL PRESSURE WITH AN INCREASE IN OIL TEMP. PRESSURE WENT DOWN TO THE TOP OF THE YELLOW ZONE; TEMP A BIT R OF CTR; NEITHER INDICATION BEING NORMAL. GAUGES STAYED AT THIS POINT. COULDN'T CONTACT CTR SO CALLED ON 121.5; RECEIVED ANOTHER CTR FREQ AND WAS GIVEN VECTOR TO WATERTOWN; NY. AFTER DSCNT OF 2000-3000 FT THE GAUGES WENT BACK TO NORMAL. REQUESTED DIRECT BURLINGTON; VT; AND CLB BACK TO ALT. AFTER ABOUT 10 MINS; GAUGES STARTED GOING TO LOWER PRESSURE AND HIGHER TEMP AGAIN; AND ON DSCNT TO BURLINGTON NORMALIZED AGAIN. LANDED WITHOUT INCIDENT IN BTV; RUNUP SHOWED NORMAL CONDITIONS. OIL LEVEL SHOWED FULL. DROPPED OFF PAX AND FLEW VFR TO MVL WITH ALL GAUGES NORMAL. CONTACTED MY MECH AND THE MOONEY FACTORY WITH BOTH EXPLAINING THE ABNORMAL GAUGE READINGS RESULTING FROM EXTREME COLD (MINUS 20 DEGS C) WHICH PARTLY CONGEALED THE OIL; RESULTING IN SLOWER FLOW THROUGH THE COOLER AND THROUGH THE ENG. THIS RESULTED IN HOTTER OIL AND LOWER PRESSURE. ACFT SUBSEQUENTLY GIVEN REGULAR 50 HR CHKUP AND FLOWN WITH EVERYTHING NORMAL. I NORMALLY OPEN THE COWL FLAPS TO STABILIZE CYLINDER TEMPS; HOWEVER; AT THIS LOW TEMP; I SHOULD HAVE HAD THEM 1/4 OPEN OR COMPLETELY CLOSED. PLTS OPERATING HANDBOOK MAKES NO MENTION OF THE POSSIBILITY OF THE OIL TEMP/PRESSURE READINGS AT LOW TEMPS.