Running hot

[Campobelloman22]

08 Cobolt running hot
6 months ago I suspected my cobalt had a
small head gasket leak due to low coolant
and some/little white smoke. I added some
expensive stop leak by manufacturers
directions and my issues went away. I've
constantly monitored my temp and it ran
from 190-205 till now. It gets up to 220-225
or hotter unless you turn the heat off and the
temperature drops below 210. I have no
coolant loss and changed the thermostat
and still have same issue. Temp actually got
up to 240 until I turned heat off. Fan appears
to be working fine. Any ideas?
2008 Chevrolet Cobalt SS Coupe

 

[YelloEye]

Welcome!

How many miles? Have you flushed the coolant?

 

[Campobelloman22]

140,000 and no I have not flushed the coolent figured that would mess my stop leak job up or will it

 

[YelloEye]

Shouldn't, though I try to stay away from the stuff as it can reduce the effectiveness of the radiator if the stuff gets stuck in there.

 

[roosterk0031]

If the heat knob is straight up or any to the right the AC is running (at least on my 09) keep it a little to the left, cranking up heat should lower temp.