Lion causes the Air to run really hot?

Check the "Activity Monitor" and find out which process is spiking the CPU.. I had the same issue and it was because of Citrix Access Gateway plugin "AGAdminservices"

I've found that Safari seems to be making things run hot on my MBA, particularly with complex web pages. I'm not seeing the same heat when I use Firefox, though. And Flash is always bringing a barrel of pain for me in Lion, regardless of the browser.

What I found interesting was that even when Spotlight was indexing, Activity Monitor didn't show any really high CPU usage (I never saw it go above 45%), despite the temp reaching up to 100°C. I was a little confused by this...

Yes this is a big problem with Lion. Older Air's run very hot with it. If you are doing very little it is fine but run Flash or some other CPU hog and your temperature will rise rapidly. I'm doing a disk copy with cccloner right now and the Air is running at 100C and has gone in to thermal shut down 8 or 9 time while doing this one disk clone.

Right now Lion is reseting the CPU parameters continualy so CoolBook isn't even an option. I think Apple have caused a big problem with this. I'm thinking I might take it into the Apple store and ask them to replace it as it is listed as a compatible system. Obviously it isn't...

I'm having the same issue with my late 2010 Air. I use iStat to keep an eye on things and with 10.6.x, I would sit around 114F even when running a Flash-heavy page or 10+ apps. Now, when sitting idle, right after boot, I am running at 124F - 130F. Last night, while trying (unsuccessfully) to make my first post-Lion Time Machine backup, It was getting all the way up to 186F. I really hope this is identified and fixed soon.

Try resetting SMC:
https://discussions.apple.com/thread/3191053?answerId=15731115022#15731115022

Same problem. VERY HOT, kernel_task eats the entire CPU. Mid-2009 MacBook Air

I have exactly the same problem.

I'am just downloading xcode from the AppStore and the CPU heats up to 80°C and fan goes to 6200rpm.

I really hope that 10.7.1 update will fix it.

Yeah, I tried that the other day with high hopes, but it had no perceivable effect, unfortunately.

Since I can't wait. Does anyone know how to downgrade to SL without data loss ?

I have only one partition and I would like to reinstall SL: compiling an hello world program is becoming as huge as compiling QTSDK...

Just out of curiosity, do you have VMware Fusion installed on your Air? I don't know if it's a coincidence, but I just disabled all of the "vmnet" processes via Activity Monitor, and now I can get through a whole Flash video without cracking 80°C.

(actually, more technically, I disabled them from starting by moving the "com.vmware.launchd.vmware.plist" file out of Library/LaunchDaemons)

Nop it's a fresh install.

I have nothing which can increase the temp like this. But, I stopped to use Chrome. When I scrolled webpages, I have noticed that it increase the temp.

Did you try to download something big such as xcode4 from the appstore ? during the download, I've a process (I don't remember the name) which takes 60% of CPU...

Yeah, I did download Xcode, and it definitely got hot in some spots (occasionally reaching 100°C for a couple seconds at a time). I'm just cleaning out as much as possible right now in terms of processes that might be running in the background, and (coincidentally or not) my heat issues have gone done. I'm wondering, though, if it's just a result of the system doing post-upgrade maintainance. Even after Spotlight finished indexing, I noticed that kernel_task continued to be rather active in terms of CPU percentage.

Yes, I've also the kernel_task process which takes CPU percentage.

Solution: kill kernel_task 😉 ?

Ha, good luck with that! 😁

I would suggest waiting it out for a day or so to see what happens. My heat issues have honestly gotten a lot better since my first 24 hours with Lion. Otherwise, I guess the best way to revert back to Snow Leopard would be to hit your Time Machine backup if you have one...