Got a P0125 code (Insufficient Coolant Temperature For Closed Loop Fuel Control) on my 2010 KIA Forte with 120k miles. I constantly needed to add coolant, heat comes on and off and the car overheated during idle and runs at high temp (225F+) during acceleration. I added a sealant, the coolant leaks stopped but now the car overheats at idle but cools down (180F) when I press on gas weather moving or stopped. Heat still comes on and off. Do just need to burp the cooling system?
It does certainly have some air trapped in the cooling system (and it could return, promptly after purging the air).
Definitely, purge the cooling system, but keep your fingers crossed!
The episodes of apparent temperature swings and the constantly needed to add coolant could have done some damage or been signs of damage not permanently fixed by mechanic-in-a-can.
For future reference, it would have been better to find the actual source of the leak and evaluate what would be needed to fix it correctly. The sealant might not work long-term and it might cause other problems by clogging up small openings.
Might be worth it to invest in a new radiator cap too, at the same time the cooling system is bled of air bubbles.
When it overheats at idle, the radiator fan should be spinning like a banshee … Is it?