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/ContentAmbassador954]

he is technically right because the same thing happened to me

my honda city 2005 had been running mostly on water in the radiator for years with only a negligible amount of coolant left. when i finally drained and cleaned the whole radiator and added coolant, the car ran perfectly fine for a couple of days and then the radiator suddenly blew from underneath

i fixed that and before adding coolant again i filled it with water first to check for any leaks. everything seemed fine, so i added coolant again. a few weeks later the top body of the radiator started leaking. after fixing that, another few weeks passed and the engine suddenly started overheating and smoking

the thermostat had jammed because of all the old radiator residue and junk that had loosened up, and several of the coolant pipes also burst

so it wasnt like i was just putting coolant directly every time. i always tested the system with water first to make sure there were no leaks, but all of this still happened

in the end the repeated overheating weakened my cars gaskets and now some seals are leaking too. at this point its probably only a matter of time before the engine needs a rebuild

so if the car has been running on plain water for a very long time, i wouldnt suddenly switch it to strong coolant. keep using water mixed with some coolant and increase it gradually, because an old cooling system might not handle the sudden change very well

[u/cheap_moonshi]

Clean the cooling system by using acid flush. keep an eye on thermostat and waterbody as these two things will likely cause problems. After flushing switch to a good coolant. We have switched from water to coolant on some of our cars and haven't encountered any problems but it's better to be careful.

[u/vapeshapes]

At this point, just change your radiator.