I have a 2005 Aveo that is not running properly. A few years back I had to change the thermostat housing as to the old plastic one breaking, I was fortunate as to the motor not blowing as I had seen with others. The car was overheating and losing antifreeze and I finally investigated and found the problem and fixed it. Since I have had coolant problems, the car is still losing antifreeze/water as was before but I do not see any leaks. I notice when the coolant gets low it starts to overheat. I am constantly adding antifreeze/water. I took off the fill bottle cap and steams comes out which tells me it is still under pressure. I have checked the oil to see if any water appears in it and it seems to be of a regular color or make up. The odd thing now is the car is starting hard and running funny, not sputter/sputtering but sputtering some. I am concerned it could be the head gasket but the oil does not indicate any liquid going there. I hate to be long in my writing but trying to give the best feed I can to get the problem analyzed. I would appreciate any help, thanks and God bless.