The car is an 04' GTP. Last year I replaced my heater core that was dumping coolant into my passenger floorboard. With the help of people on here the daunting task was still a PITA but we navigated it well and completed the process. Everything has been as good as can be expected until the last week or so.
I first noticed the car starting to get "a little" warm...just registering higher than it usually does, but no where near danger. Then it started to creep up further and gave concern so we checked and it was low on water. Addition of water and it was fine. Next day, same thing and we thought it might be the thermostat and replaced it. Problem persisted again, took thermostat completely out to see what would happen. Over the weekend took a 2 hour (each way) trip and it was fine, yesterday fine, (temperature wise) and this morning GF leaves for school, makes it 4 or 5 miles down the road and the bells and whistles go off for overheating. I get there and have to add almost a full gallon of water to it, temp goes down and I am able to get it back home.
There isn't a visible leak that I can see, I've spent time watching it running and just sitting and I cannot find one. I don't see water on the ground after it's been sitting and I can't see anything spraying out of say a hose or something. What do you guys think? Do I need to replace the water pump or is there anything else that comes to mind.
As always input and knowledge is always very appreciated.