i have a old chevy minivan i i need help trying to take out thermostat bolt it broke?

while taking the thermostat out of my old ford minivan one of the head of the bolts snapped of because it was so rusted i have the top piece of the thermostat housing of in i have about half in of the broken bolt that i can grab but i tried vise grips ,pliers, aand even pipe wrench and it wont budge its really stuck does anyone know any tricks to take it of or any tools and i have sprayed almost whole bottle of wd40
 
Back
Top