You might also have a bad heater core that needs to be replaced. You can either attempt to flush it out or just have it replaced. Heater cores are not extremely expensive, but I would recommend changing the thermostat at same time. Thermostats are normally $10 to $20 where a heater core can be anywhere past $50.
The car will over heat.
You probably have a leak in the heater core.
there might be a leak some where in a coolant line. or maybe you have a leak in your radiator.
It depends on how bad the leak is .If its a really bad leak to the point where the car is starting to overheat then no
You have to determine the source of the leak then decide on how to fix it.
For one, you probably have a leak, and also you probably have a clogged heater core.
The heater in a car is a little radiator under the dashboard. It's called the heater core. There's a valve in the water system that sends hot coolant into the heater core when you turn on the heat, and keeps the coolant in the engine when you don't want heat. If the car is leaking antifreeze when the heat is on but not when it's off, something in the heater system has a hole in it. Because there's always coolant in the heater core and the hoses that feed it, my first thought is the valve itself is bad.
cap is off
That is probably antifreeze steam. Your heater core is a small radiator used to heat your car. The engine heats the antifreeze and circulates it through the heater core. Your blower blows heat through the core (radiator) into the car, and warms you. If the core gets a small leak, it will put out steam.
water pump
Coolant leak, possible heater core. Suggest to have it pressure tested to find leak.
heater core has a pinhole leak! Only shows when under pressure .remove and replace not good to breath antifreeze vapers!