Overheating

Good morning


I need to see if you might be able to help me. I bought this car a year and a half ago. I believe it need to have the lower intake gasket replaced. how ever i think ther is a compound issue here as well. The intake gasket hasn't leaked in a really long time weird I know?? any ideas. But now I think I have a bad thermostat, i think. ...? Last night was the worst it was It just got pretty hot and would not cool down. The reservoir was filled and it just would not cool down. This morning I checked again RES. still full... I took Radiator cap off and didn't see any fluid in the raditor..untill I shook the car then down in the radiator I could see it. In the mean time as soon as I did take the radiator cap off fluid started flowing from the Resavoir into raditor? I added a little more coolant to radiator by hand untill I thought it was full. Seemed like it need it? THEN this morning it would only heat up when I stop. As soon as I started driving cooled down and heat started working. I replaced water pump about a year ago..seems to be working no leakes around it. Any help would be great it our only car.......

i don't know