Blown Engine (catastrophic failure):
* Loud knocking or rattling: This is often a very prominent sign, indicating internal damage like connecting rod failure or piston damage. It's usually a sharp, metallic sound.
* Loss of power: Significant and sudden power loss, often accompanied by other symptoms.
* Smoke (white, blue, or black, often excessive): The type of smoke can offer clues, but excessive smoke is a strong indicator of serious internal damage.
* Overheating: While overheating can occur with head gasket issues, a blown engine will likely cause severe and rapid overheating.
* Oil leaks: Significant oil leaks, possibly externally visible.
* Low oil pressure: Often indicated by a warning light.
* Visible damage: In some cases, physical damage might be visible, such as a cracked block or damaged parts.
Blown Head Gasket:
* White or milky substance in engine oil: This indicates coolant is mixing with the oil.
* White smoke from exhaust (especially when cold): This is a strong indicator of coolant leaking into the combustion chamber.
* Overheating: A frequent symptom as coolant leaks reduce the cooling system's effectiveness.
* Low coolant level: The coolant disappears without any visible leaks.
* Bubbling in the radiator: This indicates combustion pressure entering the cooling system.
* Loss of compression: This might be detected with a compression test.
* Sweet smell in the exhaust: Coolant has a slightly sweet smell that can be detected in exhaust fumes.
* Performance issues (less severe than a blown engine): Loss of power, rough running, or misfires can occur but are usually less dramatic than with a blown engine.
Overlap:
Both blown engines and blown head gaskets can cause overheating and performance issues. The key difference often lies in the *severity* and *nature* of these symptoms. A blown engine usually leads to much more dramatic and immediate problems, while a blown head gasket might present more gradually worsening symptoms.
In short: Loud knocking, immediate and significant power loss, and excessive smoke heavily suggest a blown engine. White smoke from the exhaust, milky oil, and bubbling in the radiator strongly suggest a head gasket problem.
It is crucial to have a mechanic diagnose the issue. Attempting to drive a vehicle with a blown engine or a severely damaged head gasket can cause further irreparable damage.
