I've been changing the Dex-cool every 25-30K (a bit less than a year). But I did the first change at 20,000 Miles...OMG. It was by far the worse change of all of them. The coolant coming out of the radiator itself was not horrible. However, I removed my overflow bottle, and dumped it, literally chunks came out of it....it was like jello...I could not believe my car that I owned 6 months (bought it new) and had only 20,000 miles on had such nasty *** coolant. So yea, I change it often...and like I said before, i'll be changing to the Prestone all make all model, or the peak version of it (whatever) when I hit 100K.