Direct Evidence (Requires Inspection):
* Visual Inspection: If you can visually see a crack, that's definitive proof. This often requires removing the head from the engine. Look carefully along the head's surface, especially around bolt holes, valve seats, and the combustion chambers. Cracks can be subtle, so a thorough inspection is needed, potentially with magnification.
* Pressure Test: A pressure test of the cooling system can reveal a leak. If pressure drops significantly after a period, this *suggests* a crack, but it doesn't pinpoint the location. The leak could be anywhere in the cooling system. A more specialized head-pressure test, done with the head off the block, can pinpoint a leak in the head itself.
* Dye Penetrant Test: This involves applying a dye to the head's surface, allowing it to penetrate any cracks, and then using a developer to reveal the cracks visually. This is effective for finding smaller, hard-to-see cracks.
Indirect Evidence (Symptoms):
These symptoms *suggest* a cracked head, but aren't conclusive and could indicate other problems:
* Overheating: This is a very common symptom, as coolant leaks into the combustion chamber or cylinder(s) due to the crack. The engine will overheat much more quickly and often.
* White Exhaust Smoke: If coolant is leaking into the cylinder, it will turn into steam and exit the exhaust as white smoke. This is a strong indicator, especially when accompanied by overheating.
* Loss of Coolant: A steady decrease in coolant level, without any visible external leaks, is a major red flag. The coolant is leaking internally, likely into the combustion chamber or oil.
* Milky Oil: If coolant is leaking into the crankcase (mixing with the engine oil), the oil will take on a milky appearance. This is very serious.
* Low Compression: A cracked head can cause a significant loss of compression in one or more cylinders, because the combustion chamber is not properly sealed. This requires a compression test.
* Engine Misfire: A cracked head can lead to an inconsistent or unreliable spark, resulting in a misfire, especially if coolant is interfering with the spark plug.
* Bubbling in the Radiator/Overflow Tank: When the engine is running, bubbling in the radiator or overflow tank could indicate exhaust gases entering the cooling system through a crack.
Important Note: Many of these symptoms can be caused by other issues (blown head gasket, for example). Therefore, a proper diagnosis requires a combination of observation, testing, and potentially professional assessment by a qualified mechanic. Don't attempt to diagnose or repair this yourself unless you have extensive mechanical experience. A cracked head requires significant repair, often involving head replacement or extensive repair work.
