Replaced the thermostat and everything was good no leaks. Drove it that night still nothing wrong the check engine light went out. Drove it the next day about 60 miles and went to mcdonalds sit in drive threw it started over heating and the was spying antifreeze . Took it to the shop and they said the bolt was broken on the thermostat. What could have caused this.? I know the bolt was not broken and was tighted down.

 

Have you made your own inspection of the thermostat housing? Is the bolt loose? Can you remove it?

As for reasons it is now loose, it could have broken off at the head or deeper or threads on it or in the hole for it could have been stripped. The best way to prevent bolts breaking is to chase the threads before reassembly with the bolt or a tap to make sure the threads are clean and to use a torque wrench to ensure they are not over-tightened.

 

My question being. They said it was broken.. We used the torque wrench. There was no problem. No leaks. Idk why it over heated and was blowing antifreeze. What would cause this to happen. Have changed many of these.

 

There is always a reason for everything. But sometimes those reasons are not always obvious.

Have you checked it yourself?

 

no..i have not checked it.

 

Depending on how good the original bolt was there is a lot of reasons why they could break.

Corrosion being one of them. IMHO I would go the way Christine said.
Check it out again. As you have changed it yourself also check the torque specs.
These are small bolts I would even expect torque values in in/lbs instead of ft/lbs.

A picture of the thermostat housing and the broken bolt could shed some light on why it broke.

 

Jodi, keep in mind these vehicles are nearing 20+ years old. Metal does get fatigued as it goes through the heat up and cool down cycle over the years. I'm guessing you did everything correct with torquing the bolt, but my guess is the bolt had seen its better days.

When I replace water pumps, thermostats, etc.....I always use new high grade bolts.

 

I don't chime in very much, but I'm thinking that one bolt hole could have gotten gasket material or dirt in it while doing the job and bottomed out when you torqued it down [tight enough not the leak, until it got a little over heated sitting at idle\.........and could be that the shop mechanic saw a quick fix and gave it a little more muscle and broke the bolt.............?????......I can't remember how the t stat housing is made.............

just an old man rammbling