[Bob Carriere]

some of those engine studs may actually enter into the water jacket and the end of the stud blooms with rust.

...on particularly tough broken studs I have found that in addition to welding a nut with the Mig..... I let it get cold....... then heat up the cast iron mass with the Oxy -Acet. torches..... removing a broken spring bolt stud from a HUP cast axle takes a lot of external heat.... maybe 5 or 10 minutes of heating with the torches due to the massive heat sink.

I prefer to use a box wrench and vibrate by hand back and forth. If it moves 1/16 either way you have it made. In some odd situation I welded a handle on to the nut before welding the nut on the stud..... makes it easier when doing a tractor engine in situ and the stud is in vertical position.

I have done the same thing on exhaust stud in tractor engines...uses a lot of gas but it works.

Cheers

PS..... not sure how you are making out Phil with the Polar Vortex but we now have 3 to 4 inches of fresh snow on the ground in Ottawa....... I may turn on the house Xmas lights to piss off the neighbours.