* Head Gasket Failure: This is a serious problem. A blown head gasket allows combustion gases to enter the cooling system, increasing pressure. This pressure forces coolant out of the overflow tank. Often accompanied by white smoke from the exhaust, milky oil, or overheating.
* Warped Cylinder Head: Similar to a head gasket failure, a warped cylinder head can create leaks that pressurize the cooling system.
* Cracked Cylinder Block: A crack in the engine block will also pressurize the cooling system, leading to overflow.
* Faulty Radiator Cap: A faulty radiator cap won't properly relieve pressure in the system. The pressure builds up and forces coolant out. This is a relatively inexpensive and easy fix.
* Overheating: If the engine overheats, the coolant expands significantly. This can cause it to overflow, even with a functioning radiator cap. Find the source of the overheating (thermostat, water pump, fan, low coolant).
* Cooling System Airlock: Air trapped in the cooling system can prevent proper circulation and cause pressure build-up. This usually manifests as inconsistent heating and might eventually cause overflow. Proper bleeding of the system is necessary.
* Failing Water Pump: A failing water pump might not circulate coolant effectively, leading to overheating and subsequent overflow.
* Blocked Radiator: A clogged radiator restricts coolant flow, causing overheating and pressure build-up.
Important Note: If your Aveo's antifreeze is overflowing, do not drive the car. Continuing to drive it with a pressurized cooling system could cause catastrophic engine damage. Have it inspected by a qualified mechanic as soon as possible to diagnose the root cause. Head gasket failure and cracked engine blocks are expensive repairs.
