I figured out that my glow plug controller wasnt working and decided to replace it. bought the part and, when I put a wrench around the "nut" part of the old glow plug controller, it broke off. I bypassed it with a switch but then I found that I had a coolant leak from the broken glow plug controller. I have spent the day attempting to remove what is left of the old glow plug controller and it has continued to break off, now to the point where it is flush with the block. I am thinking of continuing to try to break up the remaining aluminium with a cold chisel. Any ideas on how to get this out, without damaging the threads, and/or ending up with chunks of aluminum in my coolant system would be greatly appreciated.

 

Yeah, that's one of the flaws to that system.

If it was me I'd keep going the way you're going, chisel away the aluminum as carefully as you can to avoid the threads. But if you need to you can always run a tap through to clean it out. 1/2 NPT

May be a good time to flush your coolant, and start by using that opening as the first means of egress; forcing any chunks that fell in back out.