Ive also had temp reading problems with my E8400; i get a different reading for each core and i also get a different reading depending on which temp reading software i use : here is an example from `Core Temp` and `Real Temp`--
I read somewhere that its common for people to get inaccurate temps from the E8### chips and some people have a problem where the sensors are sticking and can get no readings at all.
Since temp readings are only a guide and not a true reflection of actual temperature, Intel will not countenance this as a problem because they dont offer temp control as part of cpu spec and modern chips have a built in shut off mechanism when a dangerous temp is reached.
I have had my chip in and out about a dozen times applying different compounds of differing amounts and ive even lapped it and always the same discrepancy between the 2 cores and the same temperatures.
I am changing my board this week so i will do a bit more lapping on the chip and heat sink but i really wont be holding my breath.