Machine yanks up ~ 100 degrees Celsius when eg. Safari is active

Hi there! I worked on this 15" late 07 MBP. Removed the MB, took out all the dust, removed the dry thermal paste & added fresh one. Cleared cashes, ran DW, DiskUtility and AppleJack -> everything is fine! But yet, u open eg, Safari (nearly idle), MacsFan Control, says the CPU temp is nearly 100 degrees C and both fans are running at 6500 rpm. Did I go wrong somewhere?

The battery is zilched out, u can use powercord only.

Any suggestions what else to do? Thanks for help

Alex the Kraut