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?

  • It might be useful to know the vehicle's model and year of manufacture
    – Zaid
    Feb 11, 2018 at 6:58
  • What is the highest temperature you are likely to see?
    – mikes
    Feb 11, 2018 at 12:12
  • Coolant prevents galvanic corrosion, water encourages it. Water is better in transporting heat, which is why it's used in combination with coolant. The life of a radiator is certainly not shortened by coolant. You can use water in an emergency, but change to coolant once you get the opportunity.
    – Bart
    Feb 11, 2018 at 15:49
  • @Zaid Mazda 323f 2000 AT.
    – L42
    Feb 12, 2018 at 5:15
  • @mikes highest is just below mid range. Not sure of the exact temperature, gauge is not digital.
    – L42
    Feb 12, 2018 at 5:18

1 Answer 1


This will depend on the car as usually now the metals used in the engine block, head and radiator with the presence of electricity can cause electrolysis ie one of the components gets “eaten”.

This is why the correct coolant type should be used - some have inhibitors designed for aluminium etc.

  • Yeah exactly what I was looking for. Are there guide like what type (brand) of coolant to be used in specific model / make of car? Or specific alloy used in radiators?
    – L42
    Feb 12, 2018 at 5:14
  • It is not the brand you should look for as most brands will sell several types of coolant inhibitor : you need to check the specs and get the correct one. Either your car manual will tell you or the dealer can or a decent store will have the charts where you look up your make and model...
    – Solar Mike
    Feb 12, 2018 at 5:17
  • Ok, so I will have to look for that before I flush and refill with coolant. Btw, I was surprise why this was marked duplicate. I think we have to be aware that although using coolant is way better, we have to choose the correct one.
    – L42
    Feb 12, 2018 at 5:21
  • And, you cannot mix them - adding an incorrect inhibitor to the correct one will cause problems.
    – Solar Mike
    Feb 12, 2018 at 5:23

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