Ziggy

It sounds like excessive voltage drop from the alt output wire to the batt.Volt drop should no more than .5 of a volt. Do you know how to check for a voltage drop? If not let me know.

I have used a product called K&W Nanotechnology Permanent Head Gasket &Block Repair. It was on 89 BMW 525. It seems to be working well no problems so far. That was last August. You have to follow the directions too the T. It's only 20.00$

Try useing a cobalt drill bit Tacoma Screw has them .

You have to use the beeswax with heat,and it wicks into the threads (I have a beeswax candle) I heat and let it cool 2 to 3 times. Be careful with Aluimium as in not getting it to hot . Drilling with L.H. bits sometimes will remove the broken bolt if you use heat around the broken bolt hole and cool the broken bolt with ice water in a squirt bottle .Also with the left hand drill bit it is turning left the way you want the bolt to go to remove it.Heating around the bolt hole makes the hole larger when it's hot and cooling the bolt shrinks it causeing some movement between the bolt and bolt hole.Once it moves, it comes out no problem . Sometimes you have to use L.H. tap and L.H. bolt . Hopefully this makes sense

Hopefully your engine is out of the car ? I would try useing left hand drill bit. And if that does not work try a L.H. tap . And if that does not work a L.H. bolt. Also use heat around bolt hole with bees wax instead of penatrating oil . Use wax when bolt is hot . not red hot , but very warm. Also when you drill a hole in the broken head bolt it takes some of pressure off the threads making it easy to remove . Make sure to drill in the very center of broken bolt . One more tip, heat around the broken bolt hole and cool the broken bolt with a ice water stream from a squirt bottle All the tools can be found on a thing called the Internet. You may have heard of it.Good luck and take your time. Drill size 19/64"and tap size 3/8" L.H.

If you use the tube cutter what size hole will it make ? I think the bolts are 6mm.If you have to completly drill the bolt out it can be repaired with a heli coil.If you use a oversize bolt the water pump mounting hole will need to be drilled out. I would try to keep it the original size . Good luck

Matco Tools sells L.H Cobalt drill bits . But you have to remove the broken bit. Or you will break the cobalt bit . Try heating the broken bolt and use some bees wax instead of penatrating oil . Use wax when bolt is hot . Also heating and cooling the bolt helps . Cool bolt with ice water from a stream of a squirt bottle .Try removing when bolt is cool and Aluminum is hot. Try this I have a few more tips if this does not work, but think it will. Don't give up !