I just put a new thermostat in my Mach 1, along with new coolant, obviously. The day after, I've only driven about a mile when I notice my temp gauge reading 240 degrees. The gauge continues going up till it hits about 280, then quickly drops to about 200. Then it slowly works its way back down to and stays at 190 degrees, which is where it should be with the new thermostat. I check everything, find no leaks, and make sure there is enough coolant. The next morning, I start it up and start driving again, and it does the same thing. It never overheats, stalls or even idles poorly when the gauge says it's running this hot. The stock gauge doesn't work, so it's got an aftermarket on on it, mounted under the dash. Is this gauge just no good, or is it really getting this hot before the thermostat opens up? Is this even typical?

 

might have had air in the system

 

it's still doing it

 

Nevermind. It is overheating and boiling over. Now I gotta find out why...

 

md told you...this is why I only buy mr gasket hipo stat..as it has a bigger ofice for more flow but it is balanced with a small hole drilled in it for that reason

 

First, make sure you put the thermostat in correctly, and not upside down. Secondly, take the cap off and let it run at idle for a long time to clear out any air in the system. In other words, burp it. Also, make sure you have enough 50/50 mixture of anti-freeze in the system. I will assume this was not happening before you changed the anti-freeze and put in the new thermostat.

 

Well from my experience, I was having a similar probolem. It did boil over. I checked everything, new thermostat. I took a close look in the radiator and relized there was a ton of buildup and deposits in the radiotor blocking the flow. New radiator, problem fixed