TbirdSCFan
Registered User
I'd start with the thermostat. Its essentially a switch... cold.. cold.. warm.. warmer... HOT! (bang Open!).. hot hot.. warmer warm.. too cold.. (close)2) That could be due to a bad sensor, a bad thermostat, or a bad gauge. I'd drain the cooling system down, pull the sending unit (the two-wire unit!), and test it or replace it (they're fairly cheap, the antifreeze you may lose will cost about as much or more than the sending unit!) If that doesn't help, pull it down again and swap the thermostat. Or if there's more than two years on the 'stat, swap it for JustIn Case (I'm starting to hate that guy ... )
RwP
This cycle repeats although not as drastic once the engine is heated up. I would recommend the Stant superstat. Its what I have in my SCs.. that is when I replace the stocker. Also, and I know there's dissagreement on it, but DO not add a bleed hole. In fact, don't buy a thermo with one. That tiny stupid hole is just enough to cause your car to underheat in cold weather.
You can test the tstat in a pot of boiling water. Start with it cold and heat it up to boiling. What you want to see is an obvious rather quick open when it gets close to boiling. and a quick close when you remove it from the water.
But, as Justin says, I'd really just replace it anyway.