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My car is running on pure distilled water in its radiator.
No winter here, so freezing the coolant wouldn't be a problem.
It is running on pure water because I'm the 2nd owner and by the time I bought it, it is already the case.
I planned on replacing it with the pre-mixed (ready to use) coolant but one of the mechanics advise not to and just leave it be if I have no problems (and actually I have no problem, haven't had any overheating issue since I bought it). He said that sometimes, new coolants doesn't help on old radiators since is shortens its life more. I got curious and search but have not seen any documentation about it.
Will it really hurt the radiator if I put coolant on it now?