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.