Had an interesting one a couple of days ago, flying out of Perth in the club Fuji FA200 (IIRC, an O320 powered beast).
Ambient temperature at ground level was -3 deg C and the engine (aircraft had been in unheated hangar overnight) was run up very gently, progressively increasing revs to around 1500 whilst at the hold, waiting for oil temp to reach 40 deg C (bottom of yellow arc). After around 10 mins running, the temp was still only 30 deg C. The pilot I was checking out (as part of club currency rules) and I agreed to proceed with the power check as the temp had not moved at all in 3 mins. After the power check, the oil temp was still only 30 deg C. We then did a couple of circuits, during which time, the oil temp dropped to 25 deg C.
I then had the aircraft booked for an XC and flew at FL60 over the Cairngorms to Inverness and back (1 hr flight either direction). At cruise power, the oil temp never rose above 25 deg C and I estimate OAT at around -16 deg C.
On paper, the flights should not have proceeded - anyone think I was doing damage to the engine by continuing?? I felt that I'd done my best to warm the engine and that a transducer positioning error was causing erroneous readings.