What could be the problem if the coolant drains fast and once it drains out the heater doesn't get hot?

There's also a smell to it, and the coolant only last for about 2 days… What culd the problem be for a 2010 ford mustang

Do you notice a puddle of coolant under the car? You should the heater core uses engine coolant to make the warm air that heats the cab if the demand switch is working & in the red. I think you have a bad leak that needs to be fixed as soon as possible! Does you're engine overheat on long drives & do you smell antifreeze all the time? If so it might be you're heater core take it to someone you trust most Ford heater cores are in the cab & the dash has to be removed. Sorry Chevy's are just as bad lol. Peace

Yes there's puddles and we do smell the antifreeze all the time… The temperature stays normal n don't over heat… Wuld you no what tha cost i wuld be facin to get it fixd.

The most obvious cause of the symptoms you describe are either a loose hose connection, a cracked hose or a leaking heater core. On a 2010 model I'd be inclined to think the hose or the connection would be more likely as heater cores generally last at least 10+ years. Also, if its the core the leak is normally first noticed inside the car on the passenger side floorboard. If its dripping outside that would be more likely to be an issue with the hoses.