I have a poorly engineered car, a 2001 Chvy Malibu. I have had problems with the entire engine temperature regulatory system and just joined a class action against GM for installing an intake manifold gasket that corrodes when in contact with Dexcool. Problem is: My engine temperature gauge does not work, the car is using gas a little fast. In the part, this was an issue with the thermostat. However, at that time, the heater did not work and this time the heater works fine. The coolant level was a little low and so I added some, but that did not work. Any ideas? Is this still the thermostat?