I agree with werxen. When you installed the HSF, what thermal paste did you use and how much did you apply? I have a Q6600 with the stock Intel HSF and a thin film of AS5 and it nerver gets hotter that 60°C at full load.
What joefriday means is that the rear case fan is inefficient because the airflow through the back is very limited. You could cut out a hole and put a mesh grille to protect the fan. That would be more efficient.
But it won't resolve your immediate high CPU temperature issue. You have to reinstall your HSF properly. Use the correct type of thermal paste (AS5 is pretty good) and only apply as much as required, i.e., a thin film like the thickness of a sheet of paper. Too much or no thermal paste causes issues like you're experiencing.
that to me looks like a dust build up problem on the CPU heatsink.
just cleanin that out should eliviate most of ur problems,
also all of the recomendations on here are good advice, so please, either replace the cooler with an after market one, or clean it and re-apply the thermal paste and then do some moddin to ur case to allow for better ventillation.