* Head Gasket Leak: This is a major problem. A blown or leaking head gasket allows coolant to leak into the combustion chamber (burning it off and causing white smoke from the exhaust) or into the oil (creating a milky, mayonnaise-like substance in the oil). This is often accompanied by overheating and loss of compression.
* Cracked Engine Block or Cylinder Head: Similar to a head gasket leak, a crack in the engine block or cylinder head allows coolant to escape. This is a very serious and expensive repair, often requiring engine replacement.
* Coolant Leak: This could be from a variety of sources, including:
* Radiator leak: Cracks, holes, or a failing radiator cap can cause coolant loss.
* Hose leak: Cracks, holes, or loose clamps on the radiator hoses, heater hoses, or other coolant lines can result in leaks.
* Water pump leak: A failing water pump can leak coolant.
* Thermostat housing leak: A crack or leak in the thermostat housing can lead to coolant loss.
* External Leak (less serious): Sometimes, a leak might be visible – look carefully under the car for puddles or signs of coolant. Check the hoses, radiator, and water pump for obvious signs of leakage.
Why the Check Engine Light?
The check engine light comes on because the car's computer detects a problem related to the cooling system. This could be:
* Low coolant level: The system's sensors detect a significant drop in coolant level.
* Overheating: The engine temperature sensor detects excessive heat.
* Other sensor issues: Problems with other sensors related to the cooling system (like the coolant temperature sensor) might trigger the light.
What to Do:
1. Do NOT drive the car: Continuing to drive with a low coolant level can cause catastrophic engine damage.
2. Have it towed to a mechanic: This is crucial to diagnose and repair the problem correctly. Attempting DIY repairs without proper diagnosis could lead to further damage and expense.
3. Check the coolant reservoir: If safe to do so (engine is off and cool), check the coolant reservoir for level and any signs of oil contamination (milky appearance).
4. Check for obvious leaks: Look for puddles under the car and examine the hoses, radiator, and water pump for any visible leaks.
Ignoring this issue will likely lead to much more expensive repairs down the line. Getting it diagnosed and fixed promptly is vital for preserving your engine.
