Last year I noticed that my Jeep would only blow out hot air if the RPM's were up above 3k. If I came to a stop it would blow out cold air. I took it to a local shop and they said my radiator was leaking and I would have to replace it...and they said I would have to change the transmission fluid since it was being contaminated. I got a second opinion from a guy I had recently became acquanted with who owns a garage. He put a pressure cap thing on the radiator and said there was absolutely no leak. He put some anti-freeze in it and it worked great. Well this year comes along and same problem. I bring it back to this guy I know and he adds more anti-freeze and the heat works great...so do I have a leak that this guy isn't noticing? Does anit-freeze need to be refilled every once and a while? Someone told me it could be a problem with the thermostat...? I just want to make sure I don't do any harm to the engine or transmission.