Here's why:
* The Coolant System and Combustion Chamber Connection: The head gasket seals the combustion chambers from the coolant passages in the engine block and cylinder head. If this gasket fails, coolant can leak into the combustion chamber.
* Combustion and Exhaust: When the engine runs, the mixture of fuel and air combusts. If coolant is in the combustion chamber, it's burned along with the fuel, turning into steam. This steam exits the engine through the exhaust system, carrying with it the antifreeze. You'll often see white, sweet-smelling exhaust as a result.
* Cracked Cylinder Head: A crack in the cylinder head can also allow coolant to mix with combustion gases and exit through the exhaust. This is a more serious problem than a blown head gasket and often requires more extensive repairs.
Other (less likely) possibilities:
While less common, other issues could *contribute* to antifreeze in the exhaust, but they usually wouldn't be the *sole* cause of a significant leak:
* Cracked Engine Block: Though less frequent than a head gasket or head crack, a crack in the engine block itself could also allow coolant to leak into the combustion chamber.
Important Note: Driving a vehicle with a blown head gasket or cracked head is extremely damaging to the engine. The continued mixing of coolant and combustion gases can cause serious internal damage, potentially leading to a catastrophic engine failure. Do not continue driving the vehicle. Have it towed to a mechanic for proper diagnosis and repair.
