A month ago i took my car to fix a little leak of coolant in the radiator, this mechanic fill it with simply water, until see if the leak was covered, well during the first 3 days the car leak a lot of water when i arrived home after work, then it stopped, i think this is because of overfilling right?

Well now i'm sure it is not leaking i'll refill with the correct mix of water and coolant, but it is working so great, the temp is so regular, that i feel nervous about changing it, i know water is so corrosive but every time i mess with the radiator problems begin...

How many days will it leak if i overfill?

The plain water isn't that corrosive. You should have the radiator full and the overflow bottle to the full mark. If it leaks with that much coolant in it you have some problems that need to be addressed.

if you were constantly just putting water in it to fill the leak over and over(always leaking), then you'd probably need to check the antifreeze freeze level. in your case though, you said it quit leaking so doing what you did was fine.

"well water" sometimes can be a little corrosive in some engines due to the particles that it can have in it. especially in diesel engines, it can cause the cylinders to pinhole but this is nothing for you to worry about.

Thanks both, i'll do th mix to have it right.
My car is so crazy (i know this sounds stupid) as some of you remember i have no thermostat, so it used to take a while to warm up, well i've noticed lately, it gets faster to the warm point and then it is ok, the first day i thought it was going to overheat, then it stoped under half (think is 210?). What i haven't checked is this. Maybe the guy who repaired the leak, uninstall this hose where the tstat goes, and then when he tried to assemble it he thought he lost the tstat and buy a new one for me...i'll check. This came to my mind right now

don't know, but i don't live in mexico city, but here in nc, our gp hardly ever moves from the 185 mark i believe.

With my 180* T-stat and PCM, the needle doesn't even go passed 180.

when there is no traffic and you could drive more than 10Km/hr mine doesnt go up 180, but driving daily more than an hour in Mexico Traffic where hardly passes 10 Km/hr and 27 celcius it gets 210 or more.

210 isn't bad 230 and up now you start to worry. Especially there in Mexico in the summer.

i never pass the 1/4 mark unless i put the a/c on and it stays on 210 i live in Phoenix so i think its ok.