Ummm, lots of P4s idle in the 50s - I see nothing wrong with that.

As I stated before, I'm not a hardware guy. I just read...
Intel® Pentium® 4 Processors - Thermal management

The internal chassis temperature for systems based on Pentium 4 processors 3 GHz (and above) should be maintained at 38°C (or lower)

Ah, I see the confusion. The internal "chassis" temperature referenced is the temperature inside the computer case, not the CPU die temperature. If you scroll down your link further, you will see Table 2. Boxed Intel Pentium 4 Processor Thermal Specifications. Note for the 3.40 CPU, the Maximum Case (and this case is that of the CPU die itself) is 70°C - making 51°C well within limits.

Very well.
I'm very well aware, you know much more about hardware, than I do, so I'm gonna keep asking questions, just to know better.

I assume, we don't want to go too close to 70C in this case, correct?
From my desktop, I know, that if I run something resources heavy, like converting video, my CPU temperature will go up about 20C.
If my idle desktop ran at 51C, I'd get dangerously close to 70C.
So, what's the solution here?

Mine Idles at about 51-52 but I have a y heat sink. Also I usually keep my fans as low as possible as I have a 120 mm fan on the back of my case that would sound like a hurricane if I turned it all the way up. I don't play heavy duty games so I'm not all that worried but I do clean it out every few months. I only worry if it gets above 65C. The P4s do heat up quite a bit and I really don't see anyone being able to "maintain" a processor at 38 unless perhaps if they are using a water cooling system. This is especially if they are talking about the temps when under a heavy load; that would be an ideal temperature. Anyway now that you know what everast says the temperature is you can run speed fan at the same time and figure out which one is the CPU temperature. I don't know if there is a way to label which temp is which in speedfan but, if you want, you can have the CPU temp as the only temp displayed.

CPU 51 °C

The questions isn't what the temperature is when your computer is idle but what it is under heavy load so I would run prime95 for 30 minutes to 1 hour to determine what the temp is under full load. I will caution you that you should stop the program if it hits 70C. Run the "torture test" and report back to us.

Originally Posted by broni

So, what's the solution here?

A better heatsink of a water cooling system. Perhaps your thermal compound isn't on correctly.

So, what's the solution here?
A better heatsink of a water cooling system. Perhaps your thermal compound isn't on correctly.

I just asked general question, because personally, I'm not facing any heat problems.

so I'm gonna keep asking questions, just to know better.

And that's fine because that forces me to double check my facts.

I assume, we don't want to go too close to 70C in this case, correct?

I don't like to see it hit 60°.

If my idle desktop ran at 51C, I'd get dangerously close to 70C.

Probably not. The difference between idle and full power temperatures is not constant. That is, 20° higher at idle does mean 20° higher maximum temperatures. Other factors come into play - fans, fan speeds, and case cooling abilities.

So, for now, I'd like to see that 51C CPU running prime95

That would be good.

If you wanna see that you need fluids.