For a self-tapping screw, wouldn't you still need to drill a hole through the middle of the broken bolt? Some of the hole saws require that you first drill a center hole. Like a spot weld saw drill bit attachment I've used before. You drill a small hole in the center, then the drill bit attachment is like a miniature hole saw with a pin in the middle to guide the cutting so it doesn't drift off. You probably can grind off the broken bolt flush, then use a center punch in the very middle of the broken bolt to mark and indent, then drill a hole through the middle of it (I don't know if you have enough room to do that). A bolt can be drilled through. What is a major pain is trying to drill through a broken bolt extractor. Those are much harder metal than a bolt.

Let us know how it turns out. I like to see photos btw. Good luck.

 

PROBLEM RESOLVED.

hi John (and everyone) - the self-tapping screw idea was a total bust - maybe partly because there wasn't enough room to apply pressure. However, I finally followed your suggestion John to take off the coolant crossover assembly (the 'gooseneck' shape seen in the pictures John provided above). It was quite easy to do! Here's a youtube video that I followed to get the assembly removed:


After removing the assembly I simply flipped it over and placed it in my drill press. The end of the broken bolt is easily visible AND it has a 'divot' which is perfect for starting a drill bit. (see pic) I used a drill bit that was about 1/16 -1/32 smaller than the diameter of the broken bolt. WORKED LIKE A CHARM. I drilled a perfectly straight hole through the broken bolt and easily fished out the remnants. I then ran a tap through the hole just to be sure, purchased a replacement bolt for <$1 from my local auto supply store and, put it back together. All is well thanks to the excellent support from John Anthony


remnants of broken bolt with the already provided divot! made using the drill press very easy

 

@deanpeddle Oh good, I'm so glad this is resolved. Great work. Yeah, that "divot" or very indented end of the bolt makes it super convenient to guide the drill so it's centered and doesn't wander off.