1978' malibu over heating problem
 

I'm fairly new to the forum and just had a quick question I've got a 78' mali running a pretty much plain jane 305. And recently with the warmer weather I have noticed it has a bit of an over heating problem. I've owned the car for about a year and a half and never had a problem besides a few wiring issues and a bad starter. But, I've noticed that after I turn off the ignition that it the water temp gauge slowly shoots to about 190-210 degrees and goes back down. But, once it passes the 180 mark the car won't turn over agian until it goes down. I'm wondering if the thermostat may be going bad? Any help would be appreciated. Thank you.