Why does my laptop get overheated when using Linux?

Hi,
I'm using a Compaq Presario cq60 and a dell Inspiron laptop. When I run them in Windows mode, the maximum core temperature it attains is around 50 (Celsius). But when I run in Linux mode sometimes the core temperature goes up to 90 (Celsius) within just, 1-2 hours. I have placed several cooling pads and sinks but seems that they are of no use.
Please help me on this issue.
Thanks.
