After you level off, the oil temperature starts coming down into the green arc. You close the cowl flaps, like you were taught to do, but the oil temperature starts climbing again. You find that it stays in the green arc if you leave the cowl flaps halfway open, but this brings the cylinder head temperature (CHT) down to a lower-than-normal reading. You know you were taught to close them during cruise, and wonder whether this extra airflow is causing some kind of thermal shock to the cylinder heads. What do you do?

You carry on with the cowl flaps half open, since this seems to be working and the cylinders might be a little cooler than before, but it doesn’t seem that significant.

You close the cowl flaps and accept a higher oil temperature in order to keep the cylinder temperatures closer to normal.