Got an Asus Radeon 3870 and I started getting some artifacts while gaming (GTAIV, The Sims 3 etc..) Eventually it got to the point where the video would cut out before I even got to my desktop. I have a well ventilated case and the card is not OC's nor does the system need to be for this to happen. Also the card it self has a pretty large Zalman heatsink/fan on it.
So I checked the temp one day with an IR Thermometer and it was reading upwards of 190 F on some points on the back of the card, Simply while in BIOS. This seems a bit high to me. I realize the card is pretty old so I have already ordered a replacement but I was wondering what would cause it to get so hot.
Btw, I checked the fan by putting it directly on 12v from the PSU and it ran at the same temps.
That is getting pretty warm. 88C isn't far from the max temp of 100C. So, the fan is turning and it is still getting that hot? For a test, you could remove the side panel of the computer and set up an external fan blowing in on it. That should cool it sufficiently. Also, did you check for dust and all? Is the HSF still firmly attached?