What kind of serious damage could have been done to our 2011 Jeep, do to continuing to drive it (to find a safe place to pull off the road),after the alarm went off and the temperature gauge was on H. It shut down and wouldn’t start again. After it sat for over an hour, while waiting for AAA, we tried to start it again and it started right up, but the antifreeze tank was empty after having been topped off a few days prior to that. It was towed to our mechanic, and he said it may have caused serious damage, because it ran on HOT & shut down. Can you please take a guess at what I can expect to be the possible type of damage, both mechanically & $$$ 😢
Yes, serious damage MAY have occurred. During overheating you can warp the cylinder head and/or engine block, damage the cylinders and pistons, burn the valves as well as a number of other things.
Did any of these happen? Your mechanic should be able to run some tests to see if there is any evidence of such damage.
I can think of 5 things that will make a cooling system work harder:
Climbing a long mountain grade/hill, and most people are totally unconscious of that. They don't realize they are on a grade. The engine is working harder and the radiator is getting less airflow since it is going slower.
Hot weather, which obviously reduces the radiator's ability to cool
High altitude - thinner air doesn't transfer heat as well
Running the "air conditioning" - the A/C condenser is in front of the radiator, so the radiator is getting hotter air and that steals from engine cooling capacity. (man, somebody ought to make an aftermarket mod to separate those two - that would be so much better).
Trailering - pulling a trailer is a much greater burden to the engine, especially on a grade.
They size cooling systems for 99% of cases. But there are "corner cases" in driving where a healthy cooling system will overload with no lasting damage if you pull over shortly after the alarms/steam. As you see on that list, it's rather easy to tick several boxes at once.
I know a mountain grade where daytime temps are often 110F, and of course everyone wants to use their A/C. (some have never not used their A/C and wouldn't know how to turn it off lol... and as said, most don't realize they're on a grade.)
However, the fact that the engine shut down is a bad omen. We hope that the modern engine control system did it to protect the engine from damage (the logic being "while you're moving, you are trying to get to a place of safety, but now you're stopped you must be at one".) But the worse explanation is that the overheat has distorted parts inside the engine, adding drag to the engine until the auto-idle control just couldn't keep the engine running. That would be more serious and could cost you at least a head gasket, and the labor of disassembling the engine that far is considerable and it would be foolish not to do a bunch of other work "while you're in there".
Low water level usually hurts the cylinder head before it hurts the short-block (where the pistons are). So "replace with a rebuilt cylinder head" may be the best way "to do all that work". That replaces the head gasket and every other gasket that might have taken heat damage, the valve seals, resolves any issues with head warpage, etc.
That is probably your worst-case scenario there.
However, you may have an abrupt failure of the car. Last time I had an overheat situation (that didn't involve loss of coolant), the cylinder head abruptly failed on me a month later. My last loss-of-coolant accident caused all the valve seals to fail.