CPU Maximum Temperatures

Excessive heat damages electronics. Monitoring the temperature of your CPU and other computer components can help you keep them running properly. To properly use most software of this type, you will need to ensure you have ACPI functionality enabled in your motherboard BIOS.

CPU temperatures can still raise if they are being used at full power for a long period of time. Using CPU's at high temperatures can lower cause system crashes in the short term and in the long term cause the life of your CPU to be greatly reduced. In extreme cases your CPU could burn out or melt onto the motherboard. This usually happens when a fan breaks down and goes unnoticed. Today's motherboards come with temperature monitoring software and hardware which actually shuts the computer off the CPU temperature gets too hot. Even these however are not 100% fail proof. The only way to be sure is to check your fans and other cooling equipment regularly and also use CPU thermometers to check your CPU temperature is stable and not raising over time. CPU's have a rated maximum temperature sometimes called a critical temperature. What this boils down to (quick pun :} ) is what the manufacturer states is the maximum temperature the CPU will operate at. This is not to say you want your CPU to operate at this temperature as it will be borderline between working and burning out. Always try to keep at least 20C below this value if you can. Below is a table showing you the critical temperatures for most of the CPU's we use today.
Please be aware that as faster models are released even under the same name the thermal requirements may change. this table is meant for a guide only and Critical temperature is often referred as Critical Case temperature as CPU core temperatures are difficult to report accurately.

CPU	Critical Temperature
AMD Athlon Series
AMD Athlon (socket) upto 1Ghz	90°C
AMD Athlon (slot) all speeds	70°C
AMD Athlon Thunderbird 1.1Ghz+	95°C
AMD Athlon MP 1.33Ghz+	95°C
AMD Athlon XP 1.33Ghz+	90°C
AMD Athlon XP T-Bred upto 2100+	90°C
AMD Athlon XP T-Bred over 2100+	85°C
AMD Athlon XP Barton	85°C
AMD Athlon 64	70°C
AMD Athlon 64 (Socket 939, 1.4 volts)	65°C
AMD Athlon 64 FX	70°C
AMD Opteron
AMD Opteron	65-71°C depending on model
AMD Sempron
AMD Sempron (T-bred/Barton core)	90°C
AMD Sempron (Paris core)	70°C
AMD Mobile Sempron	95°C
AMD Duron Series
AMD Duron up to 1Ghz	90°C
AMD Duron 1Ghz+	90°C
AMD Duron Applebred	85°C
AMD K6 Series
AMD K6/K6-2/K6-III (All except below)	70°C
AMD K6-2/K6-III (model number ending in X)	65°C
AMD K6-2+/K6-III+	85°C
Intel Pentium III Series
Pentium III Slot 1 500-866Mhz	80°C
Pentium III Slot and socket 933Mhz	75°C
Pentium III Slot 1 1Ghz	60-70°C depending on model
Pentium III Slot 1 1.13Ghz	62°C
Intel Celeron Series
Intel Celeron 266-433Mhz	85°C
Intel Celeron 466-533Mhz	70°C
Intel Celeron 566-600Mhz (Coppermine)	90°C
Intel Celeron 633-667Mhz	82°C
Intel Celeron 700Mhz+	80°C
Intel Celeron D	67°C
Intel Itanium 2
Intel Itanium 2 below 1Ghz	66°C
Intel Itanium 2 1Ghz - 1.6Ghz	83°C

source: http://www.pantherproducts.co.uk/Articles/CPU/CPU%20Temperatures.shtml