I know i have a bad head gasket, but i didn't know until the car utterly lost power one day driving it until it stalled on me. it all happened in like 10 seconds - i was going up a hill, and realized i was going too slow, tried to speed up again, and it stalled. I don't think the engine overheated. I didn't look at the temp gauge right away, but i looked at it about a minute afterwards and it was normal/low.
My mechanic is telling me that if we take the top end off only to find out that there's real damage to the block or pistons (i'm reaching a little here, not a mechanic at all myself) that would be the worst case because then i'll be paying him for the labor of tearing it down and and still throwing the whole engine away for a new one, whereas if we know it's beyond repair i can just get a new engine.
So I'm wondering if we simply start the engine - and if the engine appears run normally at least for a short while - would that mean that the engine damage is minimal and that i should expect to just have the heads machined and replace the gasket? Or is there another way to try to figure out the extent of the internal damage before doing the work of removing the heads so i can just swap the whole engine i needed?