Smells like coolant and starts to smoke out the muffler?

Hello,

When you smell coolant after turning on the heater, it usually a leaky heater core. That should be the first item to check. Usually you will have either the heater core itself that leaks of one of the hoses that goes to the heater core. The heater core is located behind the passenger side dash.

https://www.2carpros.com/articles/how-a-car-heater-works
https://www.2carpros.com/articles/replace-heater-core

Also when you mentioned smoke out of the tailpipe. What color is the smoke?
If it is whit smoke it could be a symptom of a blown head gasket. Does your engine overheats?
There is a simple test you can do to check for a blown head gasket. The test measures combustion gases in the coolant to determine if the head gasket is blown.

Here is a helpful video of how to do that test:

https://youtu.be/5zpNjYmmiYY

https://www.2carpros.com/articles/white-smoke-or-steam-coming-from-the-exhaust-pipe

I have attached diagrams for your reference.

Please let me know of any questions.

Thank you.