Welding nut on rounded engine bolt?

[Minerva]

I have a rather stubborn bolt from a leaky engine water pump. Of course the most inaccessible is jammed tight and rounded off (cheap scanners are a false economy )

I have my mig welder with me this weekend should other fettling techniques fail. Question being; should I disconnect the engine from any electrics / the batteries etc before using the welder on it?

 

[Ray Purchase]

Yes.

 

[colhel]

If it were me and if access would allow, I'd either drill or grind the head off and once the water pump is removed you might be able to get some pliers on the remaining bit of bolt. When the head of the bolt is removed there'll be no pressure on the thread making it easier to undo.

 

[Boater Sam]

Weld it,the heat will help loosen it..
Disconnect the alternator wires just to be sure.