I heard that overclocking reduces your computers life span but I was wondering how much because Ima build a new computer soon and I'm planning on overclocking the e8400 3.0ghz processor. Also, how much cooling would I need to overclock it to about 4ghz? The case I'm getting has 2 big 240mm fans on the side of the computer but I'm not sure if itll be enough since I'm new to building and overclocking.
i would recommend a xigmatek HDT-S1283 + the backplate on a budget, or the sunbeamtech core contact freezer... both available on the egg for half the price of similar performing traditional coolers
as for lifetime, assuming you stay within 1.3625 voltage intel recommends, years! it will last for much longer than you will be using it ... ie you will have a new system because the e8400 is out of date before it dies..
No one knows how much OC'ing will affect the lifespan of your CPU, as long as you don't overvolt it, it will last much longer than you'll ever need it. For a rough estimate, which has no data to back it up, I'd say your CPU would last 10 years at stock and if it was OC'd it would probably only last 8 years.
If you want to overclock, it's always intelligent to buy an aftermarket cooler. I'm not sure if you can reach 4Ghz with the stock cooler on the 8400, I would assume no.