I have a seldom used 9yo kia picanto. My sister used it last weekend and experienced overheating. She said she noticed the aircon wasn't cooling for some time and later the red temp sign lit up. She Took it to the nearest gas station and they just topped up the radiator with regular water. The aircon ran back to normal and she was able to go home. I checked today the coolant reserve level and it is full so probably no leaks. It also ran fine this afternoon when I used it for an hour with a/c on.

Should I have the coolant flushed and replaced? I'm worried the car might overheat again. I just bought 1L of abro ready mix coolant at a hardware shop (recommended over prestone). Is this enough? Can i just add distilled water? Planning to DIY coolant replacement tomorrow

thanks in advance for your advise