'05 Elantra, Erratic Heat problem

I’ve had this 05 Elantra for 3 years without trouble. This fall, it suddenly began exhibiting erratic heat problems. Sometime it’s hot, then it’s cold. It’s random. The engine temp is always stable and in the normal range. There’s no gurgling noise in the heater and the radiator overflow is full. Is there a known problem with this car? Any suggestions?

You mean it goes from hot to cold without moving the knob and in the same trip? Or some days the heat doesn’t work?

Even though the radiator overflow reservoir is full, it is possible for the cooling system to be low on coolant. If you have not yet opened the radiator cap (when the engine is cold) to check coolant level, you really need to do this.

I think that the problem could be as simple as adding coolant to the radiator. Of course, if the radiator is low on coolant, then you also have to find out where it is leaking, as coolant does not evaporate in a closed system.

Yes, it erratically goes hot and cold as I drive.

You make a good point. There have been occasions when it needed antifreeze because one clamp weeps a little bit. I hadn’t considered trapped air in the system… I need to check that out.