2005 Grand Prix:
About 9 months ago I had a problem with losing coolant. We finally found out it was leaking from the heater hose fitting so we changed both out.
This morning I started my car fine and went about 2 miles and noticed my temperature gauge start rising quickly. When it went up about halfway between the normal and red line, I pulled over to let it cool down. The hot coolant light came on and also a warning to turn off a/c to protect the engine. I did not have the a/c on but I turned it to heat to see if I could make it to the parts store about a mile away. The heat was blowing out cold so I turned it off.
I made it to the parts store and they said they couldn't check codes but since the upper hose was hot and the lower was cool, it must be a thermostat. I bought the thermostat, let the car cool down, put some water in the radiator, and started back home. I got about 2 miles away and the same overheating started. I stopped the car, cooled it down, and then went the additional mile home.
This afternoon when I got home, we switched out the thermostat. I went to add antifreeze in the radiator and noticed it was taking alot of antifreeze. Then I noticed that the antifreeze was coming out as fast as I put it in from just above the water pump from the hole where the heater hose fitting used to be. I went and got new fittings.
My question is what would cause a heater hose fitting to come off? I can't find it anywhere but it is missing. Could this have something to do with the fact that when I changed the fitting, I flushed the system and put in Dex-Cool antifreeze? We are going to change out the fittings and then check the water pump. Any suggestions on the cause of the fitting coming off?