Temp drop!why?

I have solved the problem of high temps posted earlier
but I see something I find strange:
At midday my cpu temp was 47C with my rooms temperature about 31C.
Now at 00:00 my cpu temp is 42C and my room temp 25C.
My system is cooled on air.
Is such a temp drop natural?
All this time I have been doing prime's torture test, no breaks.

of course. the difference in room temps is a huge factor.

47-31 = 16C difference
42-25 = 17C difference

Assuming the error in all your measurments was +-1C, your heatsink is performing as well in the day as the night. The temperature difference is what's important - you won't get ANY heatsink to run in a 40C case and give decent temperatures.

Bit odd the way your room has a 6C fluctuation though.

Thanks for the info guys.
Well what can I say,summers are pretty hot in Greece.
Maybe it's time to hit the beach, not the O/C limit!