Safe temperature changes (Delta T 20degrees C)

Hey Guys.

I just upgraded to a Celeron D 365 and overclocked it to 4.0ghz (upgrade serves as a hold over until i build my new computer). It's running with stock cooling and stock voltage 100% stable. My temperatures are staying well in the "safe" range (52degrees C max under full load) but the temperature drops to 31degrees C idle. At times it may make this 20degree change a few times minute (depending on the load). I've never seen this before with any of my other builds, usually I've seen a 10-15degree difference between load and idle.

Is it okay/normal for my temperature to be jumping between 32 and 52 degrees C on a regular basis? Should i cut back on the overclock. I don't want to spend any more money on this computer, as it will be replaced within a month of two and become moms computer (a slight upgrade from her P3 @ 800mhz) 8) .

Thanks for the help
Nate

70 c max 75 c - is ok

65-70c max for p4 chips - celeron is detuned p4