Hello,
I prefer to use a large screen for around 95% of the time. If I power a 27-inch Apple display with my 2012 11-inch Air shut, is the Air more likely to degrade quicker over time (i.e. the motherboard fail etc) due to higher temps with the the screen shut.
Any difference in lifespan between operating in clamshell mode or with the lid open is not significant enough for you to notice it. You will most likely replace your MBA with a newer model long before you notice any failure due to heat. While there is some heat dissipation in all directions, the primary heat removal is through the vents, located at the back of your MBA near the hinge. These vents are unobstructed with the lid open or closed. All Apple notebooks are designed to operate safely with the lid closed in clamshell mode.
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.
The bottom of your Mac notebook may become very warm during normal use. If your notebook is on your lap and gets uncomfortably warm, move it to a stable work surface that allows for good ventilation.
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), or 1200 for the newest MBAs. Older iMacs have 3 fans with minimum speeds in the 800-1200 range, while the newest iMacs have a single fan, spinning at a minimum of about 1400 rpm. 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.
For Flash-related issues:
