I am building my first computer, and I went to install my i5-2500K. After installing the CPU I went to install the CPU cooler, and realized that the package did not contain thermal paste. When I googled the product some people said the rubber like substance on the bottom of the cpu cooler was the thermal paste and that it would melt and cover the CPU after some initial use. Is this true or do I need to purchase separate thermal paste? I do not want to add thermal paste only to build up a layer too thick when combined with what may already be thermal paste on the cpu cooler.
The stuff on the bottom of the stock cooler is thermal paste, and it's not bad either. I wouldn't bother with better stuff unless you're also using a better heatsink. It definitely shouldn't be rubbery though - it should be a paste.
Aftermarket Thermal Paste will get your CPU temp down a few extra degrees but the generic paste will be fine. If you use the Artic stuff, just put a drop about the size of a pea. Its also important to have adequate airflow in your case. Good Luck!
If you plan to run the CPU at stock speeds, the stock thermal paste that is pre-applied to the heat sink is more than adequate. As long as you didn't get it dirty or anything, a little bit of dirt/oil/dust mixed in with the thermal paste can make a difference. Also verify that you have good case airflow as well, that always help.
Thanks for everyone's help (except GeekApproved who just implied I was disabled and didn't help in the least). I decided to stick with the the pre-applied paste for now and will consider new paste and a new cooler if I OC in the future.