2000 Alero Overheating when heater on

[Zait]

Odd isnt it? Browsed many times here but first time signed up and posting!

Ok, basically what is happening is when you have the heater on the car will overheat in any condition (driving streets, freeway, idle in the driveway) The thermostat creeps right on up. This just happend in the last day or so. Once you shut off the heater or switch it to a/c or to blow cold air the thermostat drops down to normal.

Normal driving without anything on the car runs fine or with the a/c on. This is only happening when the heater is engaged. There is plenty of coolant.. nothing is blocking the radiator (brush,bugs,etc) Hoses look good I cant visually see any leaks or smell anything coming from inside the vehicle or the engine area. I am at a loss.. especially since every one out there always says to turn on your heater full blast if you are having overheating issues while driving.. in this case its actually causing the problem.

I dont hear the water boiling in extreme like ive heard in some older vehicles that run hot. So im kinda torn between it actually being hot or if the thermostat has become faulty. Any suggestions would be helpful. Thanks guys.

[Iflylow]

Maybe the heater core is plugged with sludge and preventing coolant flow? Just a guess.
A bad thermostat should cause overheating all the time, not just with the heater on.

[scoopy03]

u can go to autozone or advance auto parts and let them know u want to get a heater core bypass hose. if they make u look for it look for one that u can make a u shape with. it should be like only $8-10 but $8-10 that is worth it to know if the heater core is clugged up.

[Zait]

I went down to autozone to check on the hose that you guys suggested.. the guy suggested to first try and run the heater on full blast with the radiator cap off. He said that air trapped in the system could be the cause of the problem just in the same fashion it could be if it was doing the same for the a/c. So i followed his advice out in the parking lot (before i left just in case it didnt work so i could buy the hose) I unplugged the top overflow hose and let it run until i had liquid poping out and reconnected the line. After doing so the thermostat has not passed the middle line in the past few days.

So, so far so good! If it happens again.. i will explore the bypass and check on the core.

Thanks guys.