My iMac is making lousy loud fan noise every time I turn it on and stays like that for the whole time it's on and I do not know how to fix this issue.
I have iMac, Mac OS X Lion 10.7.5, 3.06 GHz Intel Core 2 Duo.
How can I fix this problem?
First you need to determine if the fan is spinning faster because of increased heat, which is usually an indication of a heavy workload.
If you're not already doing so, use iStat Pro
(free) or iStat Menus
($16) to get accurate readings of your temps, fan speeds, etc., rather than relying on your sense of touch or sound. A forum member has posted a copy of iStat Pro that has been "tweaked" to enhance compatibility with Mountain Lion. You can download it here
The Intel processors used in Macs are designed to automatically shut down to prevent damage if they truly overheat. CPU Tjmax = 105C (221F), GPU Tjmax = 100C (212F) on i3, i5, i7 processors. (Source: Intel
Unless there is a rare defect in a Mac, most temps are well within the normal operating range, considering the workload being put on it. Websites with Flash content, games and other multimedia apps will put higher demand on the CPU/GPU, generating more heat. This is normal. If you're constantly putting high demands on your system, such as gaming or other multimedia tasks, expect temps to rise and fans to spin up accordingly. It's just your Mac doing its job to maintain temps within the normal range.
It is also quite normal for your Mac to become extremely hot to the touch during intensive operations. The aluminum body transfers heat more effectively than other materials used in computer casings, so you will feel the heat more. This doesn't indicate that it's overheating and will not harm the computer to be hot to the touch.
Your fans are always on when your Mac is on, spinning at a minimum of 2000 rpm (for MBPs) or 1800 rpm (for MBAs, MBs and minis). iMacs have 3 fans with minimum speeds in the 800-1200 range. They will spin faster as needed to keep temps at a safe level.
If your fans are spinning up without increased heat, try resetting the SMC
(PRAM/NVRAM has nothing to do with these issues, so resetting it will not help.)
The intake and exhaust vents are in the back of the computer near the hinge on all Mac notebooks (except the new MBP with retina display, which has intake vents along the sides at the bottom). The iMac vent is a slot on the back near the top of the computer. Make sure the vents remain unblocked to allow your computer to perform at its best.
Learn about the fans in your Mac
Apple Portables: Operating temperature
For Flash-related issues: