What are the symptoms of a Blown Head Gasket?

There are some makes or models of cars that have a reputation for blowing head gaskets. 

The head gasket forms a seal between the engine block and the cylinder head.  This seals both the combustion chamber and the coolant passages in your engine.  This means your head gasket has to seal both extremely hot high pressure combustion gases as well as engine coolant which can be anywhere from cold ambient temperatures to the normal operating temperature of your engine.  Do to the wide range of temperatures and relatively large surface area, it is not unusual for head gaskets to develop leaks over time.

Since the head gasket seals the coolant passage both from the atmosphere and the combustion chamber you can’t see or get too much of the head gasket on a vehicle.  Because much of the gasket can’t be seen without disassembling the engine, it can be very difficult to diagnose a head gasket leak.  Since a visual inspection usually will not prove a head gasket leak, it is important to know the other symptoms so you can accurately diagnose a head gasket problem.

Blown Head Gasket Symptoms:

Coolant leaking externally from bellow the exhaust manifold
White smoke from the exhaust pipe
Overheating engine
Bubbles in the radiator or coolant overflow tank
White milky oil
Significant loss of coolant with no visible leaks
Cracked / Blown Radiator

The only externally visible sign of a blown head gasket would be coolant externally leaking from the head gasket.  The head gasket will be below or inboard of the exhaust manifold.  Most head gasket leaks will be between the combustion chamber and the coolant passage in your engine.  On the intake stroke of the cylinder closest to the leak, coolant will be drawn in under the vacuum created along with the intake air charge.  Upon combustion, the high pressure will force exhaust gases past the head gasket into the coolant passage.  This process will repeat itself for every revolution the engine makes.

As coolant is pulled into the combustion chamber it will cause your engine coolant level to drop.  This can cause a low coolant light and overheating if the cooling system on your vehicle is not continually topped off.  Also, once your engine is turned off the coolant still left in the engine cylinder will seep past your piston rings into your engine oil.  Coolant mixed with oil will make a white milky substance.  You may see this on your engine oil dip stick or on a ring around your oil cap.

If your engine is running the small amount of coolant that is in the combustion chamber will turn into steam and white smoke upon combustion.  If you are checking your exhaust pipe for signs of white smoke, make sure your vehicle is fully warmed up and idling during a warm part of the day.  A cold engine on a cool day will produce a small amount of water vapor which will look like white smoke from your exhaust pipe.  If the exhaust has a sweet smell to it then it mostly likely is a head gasket problem.

during the combustion process the high pressures in the cylinder can push exhaust gases past the head gasket into the engine cooling system.  The exhaust gases will be trapped in the cooling system and will be circulated through your engine and into the radiator.  During normal operation your engine’s cooling system remains under pressure, so never remove the radiator cap while the engine is operating or still warm.  If your vehicle has a coolant overflow tank you can check that for the presence of bubbles.  To be certain you can purchase a test kit from your local auto parts store that will chemically check your engine coolant for the presence of exhaust gases.

Usually one of these symptoms by itself is not enough to prove you have a head gasket leak, but if you have multiple symptoms at the same time it is likely that you have a head gasket leak.  It is important to drive your vehicle as little as possible if you have a head gasket leak.  The hot gases and cold coolant moving through the hole in the gasket can quickly erode or warp the metal head or engine block leaving you with costly machining bills or even having to purchase new heads or a new engine.

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