2009 i7 iMac CPU fan speeding up

[nanosour]

I have an i7 iMac purchased in Dec 09'. Original i7 model. For the first couple years the CPU fan would max out at 2099 rpm. It was very consistent. If I put a decent GPU load on it, the fan would always max out at 2099.

Then about a year ago, I noticed the temps in the middle of the summer were running pretty high when gaming on the computer. At the suggestion of a friend, I downloaded smcfancontrol and immediately noticed the fan speed would increase to approximately 2700 rpm and become pretty loud.

Shortly after installing smcfancontrol I uninstalled it and reset the smc controller. For a while it seemed to go back to roughly 2100 rpm max. But, as of this week I saw the CPU fan at 3578 rpm! Higher than I've ever seen it. Is there a problem and is there a solution to this issue. I've done several google searches and there is so much out there for every iMac model on fan speeds.

Finally, the GPU temp was 67 C when the fan was above 3500 rpm. Not very high and the CPU temp was even lower. I'm stumped and turning to the experts on the forum.

Any help is appreciated as my warranty ran out 5 months ago!

Nano

 

[MatthewAMEL]

Well, the 1st culprit that comes to mind is airflow. If the fan is working harder to maintain temps, have you thoroughly cleaned the intake and exhaust?

That model of iMac inhales through the bottom and exhales through the top.

I use the attachment on my Dyson to vacuum both areas about once a year.

Another (controversial) culprit may be the degradation of the thermal paste.

While good quality paste like Arctic Silver doesn't degrade (it has no adhesive properties) there is some evidence that cheaper paste does degrade and loses it's efficiency at transferring heat.