GFX overheating? What is a good temperature

[Wej]

I've recently been having problems with my 7600GT where after a period in game (mainly Oblivion and HL2) the red vanishes from the palette. Usually if I exit the game, the colour returns, although sometimes this takes a few minutes.

I've since installed nTune and run the stability test, and the temperature normally is about 55 (GPU1) in Windows which seems a little high. During the stability test it gets up to around 65-70 and during this the loss of red seems to kick in. Stop the stability test and once the temperature dips below about 57/58 the red returns again.

Couple of questions: -

1. Is this running very hot? I know my airflow is not particularly good (and I had planned to improve it) but what sort of temp should I be monitoring?

2. Has anyone else had this sort of issue with loss of a primary colour, particularly as a consequence of overheating?

3. What's the best solution, fan-wise? I've got a cheapo case, and the only extra grill is at the back halfway down? Should I be sucking or blowing (oo-er)?

EDIT: I forgot to say, it's with the stock cooler. How easy is it to replace?

 

[Wej]

Yes, everything's at stock. I could position an inlet fan at the back sucking in (the PSU blows) and see if that helps, but what surprises me is that the temperature rise is only 10-15 degrees - I though most of these things were stable much higher than 70.

 

[Wej]

Unfortunately it's not possible to bring air through the front - it's a small case and there is no way to bring it in, not even with some dremelling!

 

[Wej]

But mine is losing this colour a lot lower temperature wise and is a new build, i.e. clean.

But what else could cause it, if it runs stable in Windows and this only happens in games...?