i have a 95 Monte with a 3.1 I just bought that sat for a few years, fired right up with new battery seems to run pretty good, however the temp gauge stays all the way to the LEFT on the cold side not the hot. Only time it comes up is after you park it or if you let it idle for a long time and rev it up some. The air is barely warm when you turn the heat on. I checked the radiator it's full, but looks like there's all kinds of gummed up stuff stuck to the sides from where it's sat for so long, the resivor tank is pretty well empty. My question is do you guys think the thermostat is stuck open so the water is flowing freely and not heating up? The upper radiator hose feels hot after I park it thanks in advance!

 

You may want to flush the Radiator, you can get some additive to put in it that will help with the flow and cleaning check with your Auto parts store.
Another good source is youtube they will have several videos on this subject.
Put in a new Thermostat. You can take the reservoir tank out and clean it. Take it to the Car wash and put the wand inside and clear it that way or if you have a pressure washer also. It may need new hoses also this would be a great time to change them for sure.
After all is done make sure you bleed the system so it works properly. There is a video on Youtube about that also.
Good luck. Here is a link to get you started.

 

Yepper there Jepper, it appears you T-stat is done, its last booty warming duty is something it will not be back for......