Lantra 1992. Problem with heating

Hi all

I have problem - Hyunday Lantra 1992 almost have no heating. After 10-15 min in traffic-jam inside the car I can see steam from my mouth (outside temperature -2 oC). Where at first I must check and what is your recomendations?

Sorry for my english...

Is your engine overheating or is the temperature gauge okay?  I would suggest looking at your thermostat, especially if the car is overheating.  Otherwise, it could be a plugged heater core.

Strange situation - sometimes temperature gauge shows what engine is almost overheated and after few minutes fall dawn up to half of normal temperature. Up-down.... Next week I'm goung to change cooling fluid. I don't believe what it helps, but it will be the first step. Next I'll try to check thermostat... Have you any recomendations how to check it by my self? Or leave everything to service?

The thermostat is a fairly easy job if you've ever done any car work; you may want to just replace that to start.  If that doesn't do the job, you can check other things.