Hello all, Recently got a 92' GMC Sierra 3500 which is my first truck. I have to say that, I don't know why I never thought of getting one before and how I went so long without one lol. I'm glad to be apart of the forum and already have a question for anyone willing to answer. The truck sat for six months before I bought it and was started every two weeks during that time frame. I noticed when I did a coolant flush on it that the fluid was beyond bad and brown and rust coloration. The owner said that the heater worked great before he parked it but when I got it the fan blows fine but the heater will not get hot. I asked him about it and he said that the electronic control unit in the dash may be bad. Can anyone shed some light?