I had the same problem with my 91. Had two contributing problems--------- faulty thermostat and a small leak that prevented the radiator from remaing full. The thermostat opened to early so the temperature was not hot enough and the emty space in the radiator, which was air would not heat up like water. Fixed both, haeter works fine. Joe Baiunco 89 Cabernet,black,honey 92, red, tan, honey