your right you have to watch your heat zone if its to cool your can end up with a hard spot or a weld that will not machine . i weld decks put back in oil pan rail s starter ears and cracks . i like to U groove the spot heat out with a rose bud tip to 400.then use weld mold rod rod there 700 and 702 i have had very good luck with this stuff . but some blocks just weld like crap .i do alot of peining of the weld and grinding back for clean .sound as i can weld. i tig with missle rod and nickel but there much more pre heat and cool down not really worth the time . iron filler rod can be used but you have to get every thing so hot all machine work could be screwed up from all the heat .i also use the threaded plugs /pins for small cracks