Thermostat replacement on a 2003 4.3 L V6 :there are only two bolts and both are the same thread size but I suspect one bolt is about 1/2 inch shorter that the other. This means if you swap those two bolts and get them in the wrong position, you will over tighten it and it will still leak. So you over tighten it until you snap it in half. It will then be flush with the top of the thermostat housing on the intake manifold. I cannot get Visegrip pliers on it, so I am trying to drill a hole in the center of the broken bolt to install an extraction bit. My experience is that you NEVER get the drill bit in the exact center of the broken bolt. I bought an extraction tool kit from Home Depot and so far I am not sucessful in this frustrating experience. Any ideas or suggestions are greatly appreciated. The center drilled hole is a little off center. These two 'bolts' actually look like studs, but they come out as a bolt, not a stud, if you understand my explaination. I used a deep socket to remove them.
I also want to mention a caution when buying a replacement Thermostat. Get an AC Delco not a MotoRad. All the auto parts stores had only the Motorad and no one had an AC Delco 'stat. I needed my Chevy running quickly because it is the only vehicle I have with cool Air Conditioning and I live in SC. Please take a moment to help me get my 2003 Chevy Truck back on the road..

 

Weld a nut onto the stud. The heat will hopefully help then move. You may end up needing to drill the bolt out, rethread the hole.

 

Use a Dremel to cut a groove then use a flat blade screwdriver. A hacksaw may work too, don't worry if the groove goes into the housing.

 

I thought I had mentioned that I have no welder or welding skills if I were to rent or buy one. I did watch the Eric from SMA You Tube video. He is great.
I also have no Dremel tool to cut a slot in the broken bolt and use a straight slot screw driver to turn it out. I wouldn't want to do this method because
of the fear of overcutting the slot and causing a bad leak. That would mean I would have to replace the intake manifold which is a procedure
I have never done.
I am going to try again to do the Extractor method. I may have to go to Home Depot to get another bigger set of Extractor bits and drill bits of the proper size.
This presents a problem because MY back up 'Parts Getter' car is also having mechanical problems. It is a Chevy Lumina and you don't want to know those
problems. I hate FWD cars. Enough said. I have to borrow a van from my neighbor to drive 12 milles into town to get parts or tools.
Does anyone know if the two bolts or studs that hold on the Thermostat are the same length or is one a 1/2 inch or so longer than the other ?
The stud has a 'frozen nut'/rusted/ on the threaded portion , so THAT may be what is causing what I am 'addressing' as a one fastener is 'shorter than the other'.
I hope I have previously CLEARLY explained what I think caused the fastener to initially break off in the intake manifold. i.e. overtightening due to the longer bolt
bottoming out before the nut touched the surface of the intake manifold and began to tighten to the correct 'torque'. This would mean the bolt was overtorqued
and sheared when it bottomed out prematurely in the.intake manifold. Even though it FELT properly torqued it was not compressing the thermostat housing
enough to properly seal the thermostat gasket from leaking. It was still leaking and additional tightening resulted in shearing this bolt off in the intake manifold.
Now we are again back to addressing the extration problem. THANKS for your help. Jim

 

If you need to use the extractor method, soaking it with a good penetrating fluid (regular WD40 is not the best for this) will hopefully help free the the seized bolt. Also, I've found that gently tapping the extractor tool with a hammer into the drilled hole in the bolt helps to seat the extractor, and adds a bit of shock to loosen the corrosion.

 

Sorry to tell you, but a steel bolt corroded into aluminum is what you have there. It's not coming out with an ez out or a slot/screwdriver. Find someone experienced in a shop to weld the nut on or give up on that intake manifold.

 

It sounds like OP just put the bolt in there and (over)tightened it recently. Corrosion might not be an issue.