Coolant/Engine Overheating Issues MK2

Hi,

A few months ago I noticed my coolant level was dropping a little every time I checked it (once or twice a month, I know I should be better).  It seemed like nothing too crazy, so I topped it up twice with some coolant and water.  I've been checking it since then and the level appeared to have stayed the same, so I thought nothing more of it.

This morning I took the car for a drive, after about 5 minutes (and, predictably already on the motorway), I noticed my exhaust spitting white deposits onto the back window.   A minute or so later the engineer temperature warning came on, the gauge had flown to the maximum marker and a cloud of white smoke blew from the exhaust.    I took the nearest exit and drove the car home.   I know this was a mistake and knew it even moreso when I started to hear a knocking noise every time I pressed the gas pedal.    I drove the car like that for maybe 5-10 minutes.   

When I got home I allowed the car to cool down then topped it up again with coolant.  However, this time the coolant appeared almost immediately in a puddle on the ground beneath the car.    Called the mechanic and immediately brought it in.    He repeated the top-up process and told me a pipe on the thermostat housing had broken off completely and this is where the coolant was now guzzling out of.    He replaced it and said it should be fine.

However, since returning home with the car I've noticed both the engine and exhaust are making louder than usual sounds.   The knocking sound on the accelerator has gone and there's no more white smoke.   I've left the car to cool for three/four hours, went out and let the engine idle for less than five minutes, it seems to be running to normal engine temperature incredibly quickly.

Have I completely screwed the engine by driving it home earlier in the day?   Helpful advice on what the issue could be would be gratefully accepted, as opposed to just reminding me what a total idiot I am for not immediately pulling over.

Thanks in advance

😕