What would happen is the heated element gets bent from too much travel. When the needle hits the top peg hard, it bends the element down, and the gauge reads 0 forever (since at true zero it wants to point straight down, but the bottom peg stops it at zero).

"A young man who does not have what it takes to perform military service is not likely to have what it takes to make a living." - John F. Kennedy

Proud owner of an 88 Montero (with a blown engine).