Why Did My Car's Headgasket Blow?

By Karen Johnston May 21, 2010

Quick facts

Most head gasket failures trace back to neglected coolant maintenance and acidic coolant.
Coolant should be flushed every 2 years or 30,000 miles to maintain proper pH.
Coolant pH should be maintained at 9.5. Below that it becomes corrosive to engine components.
White smoke from the tailpipe is one of the most recognizable symptoms of a blown head gasket.

What exactly does "blown" mean anyway?

The head gasket in your engine is the gasket that seals the cylinder head of the engine to the engine block. There are coolant and oil passages that transfer the oil and coolant from the engine to the head and back. The reason for these passages is for the oil to lubricate the valve train, and the coolant to remove heat from the cylinder head. The other job of the head gasket is sealing the top of the cylinder to keep the compression contained.

Causes of head gasket failure

Head gasket problems arise generally due to poor maintenance of the cooling system. Acidic coolant can begin to eat away or erode the sealing area of the coolant passages in the gasket. This can cause a weak area and a leak can start to form. The head gasket leaking can travel either internally or externally. An external leak is visible outside the engine. An internal leak means that coolant can seep into oil passages or erode the compression sealing ring in the head gasket, allowing coolant to enter the cylinder or compression to enter the cooling system. This is what we call a "blown" head gasket.

While an improperly maintained cooling system can cause head gasket failure, there are some vehicles that are simply prone to head gasket failure due to the composition of the head gasket material and overall engine design. A vehicle that has overheated due to coolant loss or a cooling system restriction or failure can also accelerate head gasket failure.

Prevention

The best way to prevent a head gasket failure is to maintain the cooling system in your vehicle. The recommended maintenance is to flush the coolant in your vehicle approximately every 2 years or every 30,000 miles. It is important to keep the coolant protection level in our climate at -34 degrees Fahrenheit. The pH balance of coolant should be at 9.5 on the pH scale. As pH drops the coolant becomes acidic and can eat away or erode gaskets, rubber, lead, solder joints, aluminum and even steel.

The other important factor is to take care of cooling system issues as soon as they present themselves. Repair coolant leaks, restrictions or malfunctions as soon as they are detected. This will help prevent coolant loss and overheating. If your vehicle does start to climb in temperature while driving, shut it down immediately and have it towed to your trusted repair facility for a diagnosis and repair.

Symptoms of head gasket failure

No heat coming from your heater
Rising temperature gauge
Boiling or percolating coolant when the engine is shut off
Loss of coolant or coolant consumption with no obvious external leaks
White smoke billowing from the tailpipe of your vehicle
A blown-out radiator
Coolant in your oil
Coolant in the spark plug holes

If you are experiencing any of these symptoms we recommend having your vehicle checked out as soon as possible. A blown head gasket repair can be very costly, so preventing a head gasket failure is definitely in your best interests.

Frequently asked questions

Common questions

Can a blown head gasket be repaired, or does the engine need to be replaced?

In most cases the head gasket can be replaced without replacing the entire engine, but the cost varies significantly by engine design. Before repair, the cylinder head must be removed and sent to a machine shop to be checked for warping and cracks. Overheating events often warp aluminum heads, which must be resurfaced or replaced before a new gasket will seal properly. On some high-mileage engines, the repair cost may approach or exceed the vehicle's value.

How quickly can overheating damage a head gasket?

Severe overheating can compromise a head gasket in a single event. When coolant boils and the engine reaches extreme temperatures, the aluminum cylinder head expands faster than the iron or steel block, causing the clamped head gasket to shift. Even a brief overheat that is caught early can begin the process. This is why the correct response to a rising temperature gauge is to pull over immediately, not to try to make it home.

Are some vehicles more prone to head gasket failure than others?

Yes. Certain engine and head gasket material combinations are known to be more susceptible. Early Subaru EJ-series engines and some Chevrolet 3.8L V6s have well-documented head gasket issues related to the original composite gasket material and coolant channel design. On these vehicles, using the correct coolant formulation and keeping flush intervals tight is especially important. A technician familiar with these patterns can advise on preventive measures.

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