Over time the additives put in there to protect against corrosion wear down, and it also becomes a bit acidic, that can damage any metal internals, eventually you could end up with a radiator full of sludge, which can let the engine overheat.

the dex crap doesnt last as long as they say. i have had a couple cars turn the coolant bottle brown and chocolate pudding the cap in 2 years. i always flush it out and use prestone extended life and change it every two to three years, depending how much you drive

IMO whatever you use, just do not mix coolant types, by types I mean do not mix a HOAT with an OAT, always bleed the air out of the system, and fill with distilled water, do not use tap water, say you use tap water, and you have a high iron content like my water does, that iron is going to help cause the protectants in the coolant to wear out faster than normal, and that can help cause the coolant to start sludging up, at least that is what I have read in a few different threads on coolant types over the years.

I'd elaborate more on coolant types such as OAT'*, and HOAT'*, but there have been plenty of threads made on this topic over the years, google search will provide you with a few good reads on those two types.
There is also IAT, but that type is the old green stuff that is high in silicates.
I've used DexCool for years, and have had no problems personally, but if there was one type of coolant that I'd recommend using if you do a full flush is Zerex G-05, I have heard nothing but good things about it.

Welcome to the forum Zach. Really some great info provided!
I also do a flush about every 2.5 years and have been impressed with this Peak Long life Coolant.
It is almost clear..can sure see if there are contaminants present!
http://www.peakauto.com/products/ant...ts/automotive/
It has kept clean the last 50k and am about to do another flush soon.