One of my Dell D630's has been overheating so I decided to take it apart and give it a clean. No problem there, I've done plenty of desktops and a couple of laptops in my time.

After removing the heatsink I clean the fan (think with dust) and its all good. However the heatsink has three 'prongs' to it, two have thermal pads covering what I assume is the GPU and something else, and the third which sits over the CPU has a very thick layer of what I assume was paste. I'd guess its about 2-3mm think certainly way more than you could ever get using a normal paste.

Its also rock hard and no amount of Isopropyl alcohol is going to shift it. I can clean the area directly above the CPU (where its much thinner) but around it is impossible. It looks like it was soft 'pad' to start with which squeezed out the sides under pressure, although its still a perfect square on the heatsink.

I've not seen this before, so am I right in thinking it was originally a pad of some sort (its the usual thermal paste grey colour) or is it likely to be something else ?

I covered the heatsink and CPU with my usual paste and put it all back together but my CPU temps are really high so I'm worried there isn't enough of a 'connection' with the standard paste. I read the pads are put on the other two 'prongs' simply because there isn't enough height in motherboard to reach the heatsink properly, so could this be the issue with the CPU as well?

Does that explanation make sense ? If so, what should I be using other than thermal paste if it needs to be higher ?

Thanks.