Inpiron 600m heat sink reseated but cpu temps jumping around

Would appreciate it if someone can point out what I can do. I have a dell inspiron 600m which is 5 years old and still serving me faithfully. I use ubuntu on it and have a cpu temp monitor app. Now I usually open it to dust out the fan vents but never touched the sync. Today I found the sync completely clogged and so I unscrewed ( making sure not to touch the part which lies just over the cpu so as to do nothing to any thermal paste but as far as I could tell , no paste was left) the sink and then blew the clogging dirt and stuff out and put it back on top of the cpu. I screwed it back and now my laptop feels less hot and more responsive but there is a problem. the cpu temperature monitor app is now jumping around. I mean it goes straight to 66 from 57 and back to to 58 and then 52 and this is weird so now the question. How much should I have tightened the heat sink screws ( which lie on the part lying above the cpu) . Have I tightened it too much ? Too little or sth else. Since I did not do anything to the thermal paste( also by looking there was none) so I believe there is something wrong I did while reseating the sink. Please help.

 

Did you renew the thermal paste between the CPU and the heatsink?

 

I did not have any at that time and I was thinking of doing it later but my chief concern is why are the temps so very jumpy and changes so suddenly and by 6-8 degrees. If I did not have the paste and it was required then it would logically mean that the temp would slowly increase and remain high and that would have made sense . But being jumpy makes no sense . Can you tell me why this is happening?

 

Software monitor at a interval from 1 to 2 seconds. Was you CPU completely idle or burn testing? With bad paste, a slight load will cause the CPU core temp to raise quickly.

For the screws, just tight it as much as you can with hand.(I never ran it with a electric one though )

Definitely renew the paste.

Edit: lifting up the heatsink will automatically reduce the function of the thermal paste as it introduce void.

 

If your heatsink is making good contact to the CPU, it should effectively act as a damper on temperature fluctuations. That your temps are bouncing around indicate that the heatsink is not making good contact with the CPU.

 

Thanks everyone, I was thinking that too so I will do it again