Here is what I have noticed on long haul (7-8ish hours) B737-900ER flights with TK, which I've done quite a bit. Yes, it is often too hot. Once I even pulled out my dive-watch from my carry-on to show them the high temperature. I cant say if this goes for their wide-body aircrafts as TK rarely use these on the routes I usually take.

1) You can usually get the cabin crew to adjust the temperature if you ask nicely. Especially if the trick "look, even the air that comes out of the air vent is HOT" works. Some times I had to ask 2-3 times, but I usually get them to adjust it.
2) If you travel in economy, sit in the back of the plane. Not only is this the area where you are most likely to get a row to yourself, but also the temperature difference between the back and middle of the plane can be massive.
3) I have only flown J a few times on the same plane, but noticed the temperature is significantly cooler in the front (similarly to the back).
4) Window seats have lower temperature around the feet than middle and aisle-seats.
5) A cold window can be nice to lean against on a night-flight, but equally uncomfortable on a day-flight if you sit on the side where the sun hits the plane.