[Kenso]

As long as the car didn't overheat, you shouldn't have to worry about BHG from this. If you lost much coolant, you may have some air in your cooling system now. I would refill/bleed the system and things should be fine (assuming it never overheated).

 

[Kenso]

Did you ever refill the cooling system? If you lost a lot of coolant through the bleed screw, it's only natural that the car will overheat due to insufficient coolant. You need to refill and bleed the system before you drive it again (assuming that you haven't done this since it wasn't mentioned).

 

[Kenso]

Why was the thermostat changed originally? Just as a maintenance item or was there any sort of cooling issue previously? Also, if an aftermarket thermostat was used, that could cause a problem (not opening properly at times). I'm sure you could get the shop that left the bleeder open to have it towed in. Just hope they have some clue what they're doing.