If your head gasket is blown, or if you think it's about to fail, our guide will help you understand the costs of fixing it. We’ll also explain a little bit about what the head gasket does, and how to prevent issues in the future.  

What is a head gasket? 

An engine or cylinder head contains the explosive power of an internal combustion engine. It is bolted to the top of the cylinder block and contains various key components that allow an engine to run.  

Because the cylinders experience very high levels of pressure, the sealing face between the cylinder head and block needs a gasket. 

This gasket, therefore, needs to cope with extremes of heat, pressure and moisture, as there are water and oil routes that also pass through it. There are various points of failure, all of which are not good for an engine’s performance.

How much does a head gasket repair cost? 

Typically a full head gasket repair in the UK can cost between £550 and £1,700. How much exactly depends on the region, type of car and whether or not the engine has overheated. 

A vehicle with an engine in any kind of ‘V’ arrangement, i.e. a V6 or V8 can cost considerably more, as they have two cylinder heads, and therefore two gaskets. In a lot of cases removing the heads is often easier with the engine out.  

Why is a new head gasket so expensive? 

As with many things on cars, it’s not the cost of parts that drives up the price of repair, it's the labour time. A new head gasket itself will usually only cost around £20, but getting to it involves stripping the engine to its component parts. 

This was bad enough back in the days of simple cars, but now with cars having all manner of complex ancillary components, and requiring special tools or procedures for many things, the cost can soon become eye-watering. 

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What are the signs of a blown head gasket? 

Some serious engine issues can irreparably damage your car if you continue driving, so it’s important to know the signs of a blown head gasket, to be able to identify if it has happened to your car. 

Reduction in engine power 

When a head gasket breaks, the seal is broken on one or more of the cylinders, this means the energy from the combusting fuel will dissipate instead of providing power for propulsion. 

Depending on where the gasket has breached, can affect how much power is lost, but typically a 4-cylinder car will be significantly down on power with a minor head gasket leak. 

Smoke from under the bonnet 

One of the things a head gasket does is seal the waterways between the cylinder head and block, if the gasket breaks at one of these locations, water from your car's coolant system will exit the engine. 

This water and coolant mixture is likely to eject as steam, due to the extremely high temperature and pressure the coolant is under. 

Milky-coloured oil 

Because the head gasket seals both oil and coolant routes between the head and cylinder block, when it breaks, coolant can mix with the car's engine oil. 

Due to the high heat and mixing action the oil experiences in normal use, the water/coolant and oil mixture becomes emulsified, creating a white-coloured foam. This foam will typically be present at the oil filler cap, and when draining the oil. 

Smoke from the exhaust 

A common symptom of a failed head gasket is steam from the exhaust, this is due to coolant getting into the combustion chamber. The coolant is evaporated into steam and forced out of the exhaust.  

Because the coolant system operates at a moderately high pressure, the coolant will continue to be forced into the cylinders until it is all gone.  

Overheating 

When the coolant is escaping, either into the engine or out into the engine bay, it will eventually run dry. At this point, it is no longer removing heat from the engine via the radiator, and the engine will begin to overheat. 

Can I drive my car with a blown head gasket? 

Because there are a few different ways a head gasket can break, there is no definitive answer. You should not drive the car more than is absolutely necessary, in any case. 

If the car is overheating or losing significant amounts of coolant, it can be very dangerous for the engine to continue driving. As the coolant is depleted, the engine will become incredibly hot. 

What will happen if I drive my car with a blown head gasket? 

It is very likely that the engine will overheat, and if driven for an extended period - this could be as little as 5 minutes if serious coolant loss occurs - then the cylinder head can warp. 

This will increase the cost of repairing your head gasket by at least twice, as the head will now need to be machined.  

In some extreme cases, the engine block can crack, resulting in an entire engine replacement being required. 

What causes a head gasket to fail? 

Generally, head gaskets fail due to some kind of excess heat within the engine. This can be caused by a lack of coolant, or by improper engine care. 

Overheating 

When an engine runs without coolant, the block and cylinder head will begin to heat up rapidly, way past the temperature at which they are supposed to operate.  

This overheating can cause warping of the components, particularly the head. When this happens, gaps can be created where the head is no longer flat, allowing the high-pressure gases to force a path through the gasket. 

Not allowing your engine to warm up 

When starting a cold engine, it is important to not over-rev until the car is up to operating temperature.  

Excessively revving a cold engine can cause concentrations of high heat, whilst other parts of the engine are still relatively cold. This causes warpage and even cracking in the extreme.  

It is recommended that you don’t allow the engine’s rpm to exceed 3,000 until the car is at operating temperature. For Petrol cars this is usually a mile or two, diesel engines can take twice as long.  

Improper engine timing 

An engine's combustion cycle is designed for maximum power generation whilst maintaining longevity. Certain faults with ignition and timing systems can cause this cycle to be slightly out of time.     

One common cause is a stretched or skipped cambelt, this can cause the valves in the engine to remain closed at a time they should be open, creating a pre-ignition problem.

This causes a spike in pressure in the engine and specifically, the gasket was not designed for, in some cases driving a gasket to fail and allow pressure to escape.

Is it a big job to replace a head gasket?

The head gasket separates the two main components in an engine, the block and the cylinder head; it, therefore, takes quite a large amount of time to complete a replacement.

The steps involved differ from car to car, as mentioned cars with engines in a ‘V’ configuration are much more time intensive to repair.

In a typical inline-engined car, a mechanic would remove all components attached to the cylinder head, which includes the intake and exhaust manifold, the turbo if fitted, the water pump, the cambelt or chain and tensioner and any other smaller components.

The head can then be removed, either with or without the camshafts depending on the engine design. Once the head gasket has been removed, the faces cleaned and the new gasket installed, the various components can be reassembled.

Does a blown head gasket mean I need a new engine?

This depends on the severity of the problem and what caused the gasket to fail. If, as mentioned above, the head gasket failure was caused by the engine overheating, then the cylinder head and block will need to be examined.

In the event that an engine has been severely overheated, the head will often be too warped to reuse. In some cases, the engine block, the main part of the engine, can crack or warp. In many cases, this will mean that these parts will need to be replaced.

How long should a head gasket last?

In many cases, if the car has been looked after, the head gasket should last for at least 100,000 miles. 

There are some exceptions to this, where manufacturers improperly specify the gasket materials, but more often than not, a head gasket will never need to be replaced, if the car is maintained and cared for properly.

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