i have a 1997 z28 and i have been having problems with the cooling system for a while. when i started the car the other day it idled a little rough like the time i had to replace my rotor cap the service engine soon like started flashing but once the ses like stopped flashing the stumbling went away and it felt like i had all my power back but then about 3 minutes later i noticed my temperature started rising and i put the heater on and it kept rising almost to the red and i noticed that the heater was blowing out cool air as it started to overheat but then i noticed that the heater would start blowing out hot air again the temp would start going back down. i have never had this problem before i have replaced the sending unit to the gauge,the upper radiator hoses flushed the radiator put a new thermostat in about 2 months ago and had the water pump replace about 2 years ago. any help would be apprieciated

 

have you tried bleeding the system it sounds like you may have some air in there

 

i have tried that and its fine i just replaced the sending unit about a week ago cause the gauge pegged out at 260 and it wasn't overheating so i replaced the unit to the gauge and up until saturday it was running fine wouldn't ever pass 180 and now all of a sudden its back to the way it was but now i notice that when it looks like its going to try and over heat it starts blowing cooler air into the car instead of hot air out of the heater i don't know if this has anything to do with it stumbling when i first start the car cause it has only been stumbling when i first start the car in the morning when the car has been sitting for more than half a day or something