[Retardo]

Don't take that car to no mechanic. It cost less than $10 to buy a thermostat. Do it yourself! If you don't know how, buy a Haynes manual for $16 at Advanced Auto. Total for the job = ~$26.. Taking it to a mechanic = $50+ for the 20 minute job.

Anyways, a thermostat stuck open won't prevent heat. The heat comes directly off the heads and flows down into the heater core, which then blows the heat into the cabin. If the thermostat was closed, the dummy light would of indicated overheating occuring, and you wouldn't have heat since no water would be able to flow. Check the thermostat.

One way to check and see if it's stuck opened is, crank up the car and let it idle for about 2-3 minutes. Squeeze the upper radiator hose. You'll be able to feel water in it if the thermo is stuck open. If you feel nothing then the thermo is fine.