I'm puzzled by the answer that Intel have given. Why is it that it is not compatible? Just over at Arctic Cooling; their products (for example the Alpine 11 Pro Rev. 2 can be used for both the E8400 and the E6850). Please explain in detail as to why the parts are not compatible. Thanks in advance.
Each processor has its own designed cooling solution.
Comparing the Intel® Core™ 2 Duo Processor E8400 and the Intel® Core™ 2 Duo Processor E6850, they are designed with a different lithography; the Intel® Core™ 2 Duo E8400 is a 45nm processor while the Intel® Core™ 2 Duo E6850 is a 65nm. Due to this, the cooling solution between them differs.
Intel® Core™ 2 Duo Processor E8400 uses fan part number E33681-001 and E97375-001.
Intel® Core™ 2 Duo Processor E6850 uses fan part number D60188-001.