On the PB4Y conversions, we could easily lean by exhaust color at night; it was as effective as leaning by instrumentation. The short stacks on the R2600's showed the exhaust flame clearly, as did the collector. If one leaned until the flame changed from yellow to a cool blue and then leaned to adjust the length along with power, one could set the mixture fairly accurately, as evidenced by engine instrumentation.
Well surely that proves the point beyond doubt that waiting for the oil temperature to rise into the green sector before engine run-up or take off on these aircraft types, is unnecessary; and may even be counter-productive with regards to engine overheating possibility.
I've replaced crankshaft seals on more than a few occasions on light airplanes when people failed to allow the oil to warm before takeoff.
Another factor not often realised by private pilots, is that as cylinder temperatures rise caused by lack of cooling airflow through the cowls on the ground, there is a steady loss of power due to hotter and less dense fuel entering each cylinder. This shows up in the minimum static RPM test if one is carried out.
It really doesn't.
Unless one is drawing air from within the cowling area (such as a carburetor heat test), one doesn't see a significant increase in induction air temperature...certainly not as a result of cylinder temperature. Further, static RPM isn't decreased by CHT during ground operations.