Is engine code P00B7 and expensive fix? I bought an ATS new in 14. It now has 73k miles on it. I'm burning off about a gallon of coolant/antifreeze every 24-36 hours. Also just started leaking. It'* at the dealer now out of warranty. What am I in for here? From all I've read this is very serious. Should I sell the car? Will this be astronomical to fix?

Any feedback is appreciated.

That code is for low engine coolant flow. Impossible to tell how expensive the fix is without further diagnostics. Could be a bad water pump, plugged radiator, or something more serious. What is the dealership telling you?

Could be the thermostat isn't opening up completely which is causing the coolant within the engine to become too hot creating excessive coolant system pressure resulting in the coolant escaping (as steam) out of the coolant fill tank.

Stuck thermostat results in Low Coolant Flow.
Low coolant flow causing excessive coolant temp resulting loss of coolant.

I'd remove the thermostat, clear the code and see if the P00B7 code comes back. If it doesn't, you could assume that you have a faulty thermostat.

If the P00B7 code comes back (with the thermostat removed) you can assume the thermostat is good and something else is at fault. Note: if you remove the thermostat, you will get a different code related to the Engine Coolant Temperature Sensor (and again, you will need to clear the code).

look closely at the radiator for a coolant leak, you can remove the plastic panel at the front of the engine bay to get a good look