If it is "close" to home, I think they could drive it safely.

They would have to let it cool off completely, then drive it ONLY until it hits approx 105deg. Then they need to immediately shut it off (stop for lunch, etc) and wait an hour before driving it again.

It's easier to tow it, but if they are a reasonable distance from home, they can do it without causing much further damage. I say this, because if the head is already cracked it isn't going to get any "more cracked"

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