ATI Radeon HD 4850 idle temps creeping up

Hello,

I built a new PC around September of last year and got the VGA SAPPHIRE 100242L HD4850 512M RT from Newegg. I know the card runs hot, but here 6 months later I find the idle temp on my card going higher and higher.

First it started idling at 80C, which I was fine with, I know the card runs hot. But progressively the idle temp kept going up, 81, 82, 83, etc and now the card is idling at 85-86C after 6 months; while I am just in Windows, not even playing any games.

I opened the case and checked for dust on the fan etc, and found almost no dust or anything like this so I don't think that is the problem.

Is my card defective, and if not why does my idle temp keep going up over time?

Thanks for any help and advice.