1. Easy Methods (Try these first):
* Penetrating Oil: This is your first line of defense. Liberally apply a good penetrating oil (like PB Blaster, Kroil, or Liquid Wrench) to the broken bolt. Let it soak for *at least* 30 minutes, preferably overnight. Reapply several times. This helps break down rust and corrosion, allowing the remaining portion of the bolt to turn. Try using pliers or vice grips after the soak.
* Left-Hand Drill Bit: If the bolt is sticking up enough, a left-hand drill bit (slightly smaller than the bolt diameter) might work. The reverse threads will grip the broken bolt and, with careful turning, may back it out. Go slowly and use plenty of cutting fluid. This is a higher risk method.
2. More Involved Methods (If the above fail):
* Bolt Extractor: These are specialized tools with reverse threads that grip into the broken bolt. They come in various sizes and types (e.g., screw-type, hammer-type). This is generally a good solution, but choosing the correct size is crucial. Too small, and it won't grip. Too large, and you risk damaging the housing further.
* Weld a Nut: If you have access to a welder, you can weld a nut onto the broken bolt. Make sure the weld is strong and cools completely before attempting to remove it with a wrench. This is less risky than drilling, but still requires skill.
* Drilling and Extracting (Most Involved): This is a last resort. You'll need to carefully drill a pilot hole in the center of the broken bolt, then use progressively larger drill bits to get as close as possible to the size of the bolt's original diameter. Be extremely careful not to drill into the thermostat housing itself! Once you've drilled it out as much as possible, then you use an easy out or bolt extractor. If the bolt is in a tight location, this is best left to a machine shop, because damaging the housing means more work and expense.
Important Considerations:
* Access: How much access do you have to the broken bolt? Limited access might make some of these methods difficult or impossible.
* Material: Is the thermostat housing made of aluminum or something else? Aluminum is softer and more easily damaged.
* Safety: Always wear safety glasses when drilling or using power tools.
* Professional Help: If you're uncomfortable with any of these methods, don't hesitate to take it to a mechanic. The cost of repair will likely be less than the cost of replacing the entire thermostat housing.
Before you start:
* Identify the bolt size and material: This will help in selecting the correct tools and techniques.
* Take Pictures: Before you start, take detailed pictures to help you remember the assembly process later.
Remember, patience and careful work are key. Rushing can lead to further damage. Start with the easiest methods and work your way up, only resorting to more destructive methods if absolutely necessary.
