For pistons, no takeoff before oil temp in the green
From the Cessna Model 152 POH Section 5 normal Procedures page 4-23.
Quote:
"During cold weather operations no indication will be apparent on the oil temperature gauge prior to take off if the outside air temperatures are very cold. After a suitable warm up period (2-5 minutes at 1000RPM) accelerate the engine several times to a higher RPM. if the engine accelerates smoothly and oil pressure remains normal and steady, the airplane is ready for take off."
In other words no requirement to have the oil temp in the green. In fact, if you operate the engine on the ground for an extensive period in order to get the oil temperature in the green, it introduces another problem and that is lack of effective cooling airflow over the engine which can result in long term heat damage to leads and components in the engine bay.
From the above, it is probably unwise to generalise "for pistons, no take off before oil temp in the green."
