Open the Activity Monitor utility, select "All Processes" from the drop-down menu in the toolbar, and then click the "%CPU" column heading to sort all processes by the processor usage. With this sorting, are any processes regularly using a high percentage of the CPU? If so then they will be listed at the top or bottom (depening on whether you sorted ascending or decending), so note them and reply back here with what they are.
It would also help to know quantitatively what you call "too hot". Try using Marcel Bresink's Temperature Monitor to be able to read the various sensors in the Mac: http://www.bresink.com/osx/TemperatureMonitor.html