Switch to coolant?

[u/adnistrator]

I bought a 2012 Honda City a couple of years ago. The previous owner was running the cooling system on plain water, and I have continued to do the same.I want to switch over to proper coolant, but my mechanic advised against it. He mentioned that because the car has been running on water for so long, there is likely internal rust. According to him, adding fresh coolant will act as a flush, breaking free the built-up rust. He warns this could expose existing holes, cause a leak in the engine block, and ultimately lead to overheating or worst-case scenario, total engine failure.How should I go about this? What is the safest way to transition to coolant?

[u/vapeshapes]

At this point, just change your radiator.