Except for the MDDs, there are no software accessible sensors in the G4 processor.
One sure way to help cooling is to remove the old, baked out thermal pad and apply new thermal compound.
Use Arctic Cooling MX-3 or MX-4 for safe, high performance thermal conductivity.
I have found that the best temperature sensor for the G4 Quicksilver is your hand - placed gently on the processor heat sink. The dual processor models tend to run hot, and if your hand finds the heat sink too hot to hold onto, you may want to fit a slightly more powerful CPU fan such as the Evercool EC6025H12CA from
Price is c.$6.95 +s&h, and fitting it requires replacing the stock fan inside the small black cooling shroud (several Phillips head screws) pushing the blue third wire out of the way and reversing the red and black wires in the connector that connects to the two pins on the motherboard. (This gets the ground right.) A small pick or other small sharp pointed object - even a paperclip - is helpful.
Cools it right down. I never needed it on my 933MHz QS, but my dual 1GHz seems grateful.
You may also want to hold your hand behind the power supply vent just over the power cord from time to time to get a baseline on how warm your Mac is running.
By all means replace the thermal compound as Japamac recommends, and blow out the dust bunnies on a regular basis.
A cool Mac is a happy Mac!
I remove the SuperDrive and put a fan in place of it the case itself has relly bad air flow all the hot air form the CPU go right in to the power supply and the fan that in the power supply I don't think it can keep up with all that heat so win put another fan it help cool down a lot better before I did this the heat inside was 150F and after I put the fan in it now 105F and the performance is a lot better
Ok will I know fore a fact that the computer will not shut down if it overheat because the first time I ever pull apart the computer and put it back together I forgot to plug one of the fan in and it burn up the CPU and there is no thermal management if there was thay wood have made a gadget for it so you can see the temp and as far as it goes with performance I benchmark my computer before I put the fan in and after and the performance was a lot better and if you think about it look at the G5 and the cooling unit on it and how thay redirect the air flow