Well, if my CPU-temperature is at about 57°C or slightly above, the kernel forces a shutdown.
Log says:

kernel ACPI Warning (acpi_thermal-0470): Critical trip point [20060127]
kernel ACPI Warning (acpi_thermal-0644): Unable to turn cooling device [dfd88ba0] 'on' [20060127]
kernel Critical temperature reached (86 C), shutting down.
init Switching to runlevel: 0
kernel Critical temperature reached (57 C), shutting down.

I have no idea where it takes the 86° from, though. It certainly isn't that hot in there, checked it

Would be really nice if someone could tell me how to set the critical temperature higher. Seems like the guys over at Novell have overdone it a little, as I surely don't view that temperature as critical, and this is just a little bit annoying.

Check you BIOS settings. You may have the "critical temperature" set there.

Also, check your CPU chip vendor's documentation. 86 C is very high for most CPU chips, and continued running at that temperature can severely reduce your CPU's "life expectancy."

No, the BIOS setting is at 70°C, and as I said, 86° is just a blatant lie, I don't know how the kernel came up with that. (And it's telling me that every time)
The temperature at the time of the shutdown really is just 57-58, at least that's what the BIOS says, and besides, I would smell it if it weren't.

Not so fast... the internal temperature sensors could well be more accurate than your hand!

I would begin... with a very cheap fan. If you don't have one sitting on top of the CPU, add one. Make sure also that the fan(s) in the case are not obstructed, say with dust or hair or debris. (Open the case and look! Computers can be very gnarly inside.)

Now I'm pretty sure I have a fan in there, because some time ago I had to replace my old one, which didn't feel like working fulltime anymore, which resulted in the CPU going up to 90° if I was away and had bad luck
Besides, I'm also pretty sure that without a fan I would not be able to write right now ^_^
You can say that again. I regularly change some stuff inside, so I'm pretty well accustomed to that. And yes, I did clean the fan, although I'm a 100% sure that it doesn't have anything to do with it, as this temperature is normal. Only now, dear SUSE kernel doesn't see it that way.

Well, what I really just wanted to say is: I'm not an inexperienced user, so you guys don't have to treat me like one, even if it is with the best intentions
I'm just no kernel geek, that's why I am asking that question.
(Maybe I should start writing all technical? ^^)

O.K., install GKrellM and set it up to monitor your CPU and case temperatures. See if it reports the same temp as your BIOS or the SuSE kernel. It's possible (but not too likely) that the kernel has identified the temp sensor incorrectly and is, therefore, reading it wrong. The GKrellM configuration should show you what sensor(s) are detected, and what they read.

Also, check dmesg to confirm that SuSE configured everything correctly. (dmesg is what's used in Fedora -- SuSE may just put the boot log in /var/logs somewhere.)

Well, it says 56°C, as do ksensors and ksysguard (thermal_zone).

And yes, everything was configured correctly (apart from my monitor, but this is normal).

Looking at the logfiles, two questions form in my mind: 1. Where the hell does it get the 86° from? and 2. Is it forcing a shutdown because of the falsely read 86° or because of the correctly read 57°? The second options seems somewhat unlikely, but then, why is it listed as a critical temperature by the kernel?

At this point, I'm stumped. And, in fact, have about the same questions you have.

As you may have noticed, I use Fedora, not SuSE. And I haven't seen any threads about temperature problems in the Fedora forum.

Some threads you might want to look at (From a search for "temperature" and "suse"):

SuSE 10 turns off suddenly
System shutsdown due to CPU temperature
APCI problems in SuSE 10
Computer switched off suddenly (Power supply problems)
critical temerature reached shutting down (How to boot without APCI and APM)

The last one is, I think, an answer to your original question.

Odd. All these problems in the threads you found occured when using SUSE 10.0, and I did not have any problems with it. Nor with any other distro so far, for that matter. Well, who knows.

I'll try the solution from that last thread.
Thanks