Your vehicle's head gasket is an essential part of the internal combustion process. 

When a head gasket blows, this can significantly impact your engine's performance and lifespan. 

You will need to book a head gasket repair if this happens to your car.

Read on and find out what causes a blown head gasket, what it sounds like and what some of the most common symptoms of a blown head gasket are. 


What Causes a Blown Head Gasket?

A blown head gasket occurs when the seal between the engine block and the cylinder head wears away.

The previously sealed coolant and oil return passages may be impacted, and these liquids can leak into the cylinders.

This is usually caused by an overheating engine, as the increase in thermal pressure puts additional strain on the head gasket.

A head gasket could blow also due to issues with the cooling system or coolant.

Some vehicles have a coolant level warning light which can indicate that there is a problem with the head gasket.

Alternatively, there could be a problem with pre-ignition, which can cause fuel leaks if combustion does not happen when it is supposed to.

A blown head gasket is never a good sign – and will need to be checked out by a professional mechanic during a head gasket repair


Don't know your vehicle registration?
General Repair


What Does It Sound Like?

Due to the fact that the combustion chamber is improperly sealed, the combustion of fuel and air will be limited.

You may notice that the performance of your vehicle has worsened as a result.

You may even hear an exhaust leak or rough idling noise – a clear indication of a blown head gasket.

When your head gasket fails, the pressure within the cylinders will not be at the correct level.

You may hear a knocking sound emanating from the engine, or the sound of a misfire – depending on how the head gasket blew.

The sound of a misfire could be related to an overheating engine, coolant leak or lowered compression because of rough idling.

You are likely to hear a misfire during ignition if your car has a head gasket failure, particularly when you restart the car.


Signs of a Blown Head Gasket

Some of the most common signs of a blown head gasket include:

  • White exhaust smoke
  • Loss of coolant (with no obvious leaks)
  • Milky white oil
  • Bubbling in the coolant reservoir or radiator
  • Engine gauge shows maximum temperature (quickly)
  • Overheating engine
  • Loss of power

If you notice any of the above blown head gasket symptoms, you should book a repair imminently. 

You may notice clouds of sweet-smelling white exhaust smoke if you have a bad head gasket.

The smoke is caused by antifreeze leaking past the gasket and cylinders.

A leak from an oil passage to the cylinder could also cause blue smoke – though this is less common.

If a cylinder head gasket blows between the water or oil passage and the outside of the engine, this can also result in a coolant or oil leak.

When the coolant level drops, this can cause serious engine issues.

Milky sludge on the underside of the oil filler cap or the dipstick – sometimes referred to as ‘mayonnaise’ - can also indicate head gasket failure.

This is caused by coolant getting into the oil, or oil getting into the coolant.

If you continue to drive your car in this state, the antifreeze that will have contaminated the oil will ruin the engine’s bearings.

A mechanic needs to carry out an engine oil flush and to replace the oil filter.

An overheating engine – because of a clogged radiator, faulty fan, or coolant leak - can cause head gasket failure.

However, a blown head gasket can also cause the engine to overheat.

Hot exhaust gases can leak into the cooling system or coolant can leak into the cylinders to be burned off as steam – both cases resulting in an overheating engine.

If you drive while the car is overheating, this can cause alloy cylinder head warping or steam damage to the catalytic converter – ramping up the repair costs.


What Can Be Mistaken for a Blown Head Gasket?

The most common misdiagnoses of a blown head gasket are disappearing coolant and an engine that seems to be overheating for no apparent reason.

To determine the exact cause, try refilling your cooling system to see if this keeps your car cool.

If it does so for several days, then you likely only have a coolant leak.

Coolant leaks are often hard to identify, as coolant escapes the vehicle as steam – rather than leaving behind residue, as an oil leak would do.

It is possible that the coolant leak only occurs when the car is operating at temperature or when you are driving, making it especially difficult to spot.

To be certain, you can add UV dye to your cooling system and continue to drive normally for a few days.

Park your car in a dark place – like a garage at night – and search the engine bay for the dye.

The dye will light up under a UV flashlight to show you where the leak is, assuring you that you don’t just have a blown head gasket.

A blown head gasket can also be misdiagnosed if you have a rough or poorly running engine.

If you do have a blown head gasket, the coolant leaking into the combustion chamber will make combustion difficult.

It will cause engine misfires, poor idling and bad fuel economy.

This can be hard to identify, as a poorly tuned engine or dirty engine will run the same way as if there was a blown head gasket.

You should have your vehicle looked at by a professional garage to get to the root cause of the issue.


Don't know your vehicle registration?
General Repair


How Long Can You Drive?

Whilst you technically can drive with a blown head gasket, we would strongly advise against doing so.

You will feel a significant loss of power as the pressure in the combustion chamber will have been lost.

Your engine may also overheat if the blown head gasket is causing coolant to leak, which can cause further cracking and irreparable damage to the engine.

Depending on the severity of the leak or perforation, your car may only last for up to a month with a blown head gasket.

We would strongly advise that you do not continue to drive the vehicle until you have the issue causing the head gasket to fail resolved.


How Do You Prevent a Blown Head Gasket?

The best way to prevent head gasket failure is by making sure you keep your car’s coolant levels topped up.

You should also ensure that the radiator is working well and there are no leaks present.

Be sure to follow these steps regularly to further the head gasket's lifespan:

  • Use high-quality coolant
  • Book in for a car service regularly
  • Inspect and replace belts and hoses
  • Have your head gasket professionally installed


Is a Blown Head Gasket Serious?

Yes, a blown head gasket is a serious issue which you should have looked at right away.

It can cause damage to non-lubricated bearings and overheating parts, eventually causing your engine to be damaged beyond repair.


Should I Use Head Gasket Sealer?

You can pour head gasket sealer into your radiator.

After leaving the car to run for between 15 and 30 minutes with the heater and fan on at a high temperature, these sealants will heat up and begin to fill any small cracks in the head gasket.

However, you should only view this as a temporary solution to the problem.

A head gasket replacement is the only real solution, and it is better to act quickly than to deal with a more costly repair later down the line.


Don't know your vehicle registration?
General Repair


Be sure to book a head gasket repair if you notice any blown head gasket symptoms.