the thing is: i start the car, engine warms up, but the heater is cold. it heats up when i drive. is it thermostat??
thanks

 

The thermostat is designed to start opening up between 76 & 80 celsius (169-176F), and be fully open at 90c (194F). Unless the air temperature is warm, your engine doesn't get really warm during idle. The heater cannot receive hot air from the cooling system until the thermostat opens up.

If your engine is not overheating, there is nothing wrong with your thermostat.

You really shouldn't just let your engine warm up by just sitting and idling. This wastes gas and results in fuel dilution in your oil.