Roger Roger
Bottom of the list
Yeah I'm gonna go with high oil temperature as the cause of your anomaly. Like I said you could try a thicker weight of oil or a multi grade and see if it makes a difference.Glider tugs cruise for about 10 seconds before diving and driving for the field, so I have no idea. Mostly try to keep it from cooling - but 180-190 on the way down is typical.
As always, without putting hands and tools on the airplane there's a pretty good chance that I'm totally wrong.