2003 Malibu heater doesn't warm the cabin

It is blowing warm air, but the cabin never seems to get warm. The temp gauge also is always only one or two ticks above the bottom mark. Rarely does it get past the quarter mark. Now that may be because it is winter but it seemed last winter that the car was warmer than that. Is it possible that the thermostat is stuck open? Any thoughts will help.

Sounds like the thermostat is stuck open. First check though is to make sure its full, then bleed the air if you have a bleeder, I don't remember if you do or not. If air is in the system, the heater is the first place you will tell it.
If it is the thermostat, wait till its cold then you can pull the throttle body and get to the thermostat there. It is right behind the exhaust crossover pipe though, so let it cool.

I went to replace the thermostat last weekend and decided I would wait for warmer weather. The exhaust crossover pipe makes it next to impossible to get to one of the bolts and I don't feel like wrestling with it until spring. I guess we'll stay bundled up until then. Thanks!:runaround:

Take the heat shield off. The pipe is not in the way. I have small fingers and can do it without taking anything off, but if you take the shield off it gives enough room. Just take the throttle body off and then the thermostat. It is about a twenty or thirty minute job if you are good with a wrench.

You definitely want to replace the t-stat if it is stuck open and the engine is not reaching normal operating temperature. A good time to replace you coolant and flush the cooling system if you have not done so already. Pick the January thaw (which might be this weekend some places) to do it.

Beyond personal comfort, you will likely see your fuel economy suffer (by perhaps as much as 10% or more due to running rich in warm-up mode much longer than it should) and over the long haul you may see reduced life of your O2 sensor.

Thanks for all the help. I finally replaced the tstat when the fuel pressure regulator went out! Because that meant removing everything anyway, I decided to do two jobs at once. Within an hour, everything was done and we were on our way to the city. It was amazing the difference it made. In 5 minutes, we actually had to turn the heat down. Thanks again!

Good on you. Happy motoring