When you have a bad engine seal this happens
1) hard starts from wet plugs
2) steamy coolant smelling exhaust
3) when its really bad drops of dirty coolant blast out the exhaust
4) while driving the combustion will heat the system and cause it to overflow out of the reservoir once the temps rise past about the 3/4 mark. The combustion gases blow into the system causing the temps and pressure to rise which results in the overflow problem.

I doubt the mechanic is a moron. He should of pressurized the system which should expose any leaking hoses.

FWIW these cars have good power with low compression or warped housings which is why a compression test and pressure test are standard before buying one.

Easy self test. Start the car and remove the coolant fill neck top and once the thermosat opens (at about 185f) look for a constant stream of bubbles rising to the top which results from the combustion gases/exhaust blowing past the seals and into the cooling system.

I think you had a bad engine from the get go and after cruising for a while the problem became worse. If the temp went to 245f and stayed there for 5 plus minutes your engine is most likely toast. That's basically about the 3/4 mark and up on the stock gauge.

Hopefully it's just a leak in one of the hoses but again I don't think the mechanic is that stupid.

BTW I wish you all the luck in the world and safe trip home

 

Used is used when it comes to a car dealership. Buy a new car, drive it off the lot and bring it back within an hour wanting to return it, I guarantee it will be considered more used than new and will automatically lose some of it's value.