I replaced the thermostat in my 2008 GMC Acadia and it stayed _around for a while now its starting to over heat again to around 230 degrees. If I turn the heat on to 90degrees it goes back down to around 210, but if I turn heat off it shoots back up. I think its water pump but it looks like its still pumping, when I reveal the gas up it moves the water up out of radiator when I take the cap of. Can someone help me out, I'm disabled and can't afford a lot to repair it do to being on fixed income.

 

SMH...