My ex-wife ruined my Mazda 626 in a similar fashion. She was on a turnpike, running 75+ mph. She started smelling something, but she kept on driving. She noticed the car seemed to be losing power, so what does she do? She gives it more gas. Finally it is losing so much power that she can't maintain her speed, so what does she do? She continues to drive on the shoulder of the road. Finally, the engine dies. She calls me. Her comment "Well, the warning light never came on". It didn't matter that the car did not have temperature warning lights. It had gauges, that I'm certain were pegged into the red.
That little ordeal cost me a lot of money. You guessed it....warped heads, no combustion.
Notice I said she is now my ex-.