try sisoftware sandra, its a benchmarking software, theres a benchmark called processor arithmetic which maxes out my cpu to 100% (both cores, and ive got a e6300 overclocked to 3ghz from 1.8ghz). Theres also tool within sandra called burn in computer , only select proccessor arithmetic from that list if you want it constantly at 100% and then run it.
you can download it here
http://www.sisoftware.net/index.html?dir=dload&location=sware_dl_3264&langx=en&a=