Cylinder Head Gasket Replacement

Typical Cost: Medium- High
Mobile Repair? Yes
Typical Lead Time: 48-72 hours

What does a head gasket do?

The head gasket on an engine provides the seal between the engine block and the cylinder head to maintain compression and prevent the engine oil mixing with the coolant.

How does a head gasket work and what are the components?

Cylinder head gaskets are typically made from multiple thin layers, normally steel and elastomer, known as multi-layer steel (MLS) gaskets. Other substances are being used, but this is the most common.

The cylinder head gasket is positioned precisely between the faces of the top of the cylinder black and the base of the cylinder head. The cylinder head is then tightened down onto the block with cylinder head bolts which are torqued to a specific force depicted by the manufacturer. Once this is done, the gasket should seal the top and bottom halves of the engine together.

Typical symptoms that require a head gasket replacement.

In most cases the symptoms of a cylinder head gasket are pretty apparent, some however take a little know how and some tools to confirm. Typical symptoms though are;

• A cream-like colour and consistency in the oil (usually seen on the engine oil dipstick) or in the cooling system header tank.
• Coolant overflowing out of the cooling system header tank.
• An unexplained loss of coolant.
• Difficulty in starting the engine.
• Evidence of exhaust gasses in the cooling system.
• Poor engine compression.

What happens during a head gasket replacement?

There are differences between engines on the exact process and components, but the typical engine will require most of the following basics to be done

• Mechanic will check that the head gasket is faulty.
• The engine will be drained of oil and coolant.
• Components will be removed to allow access to the rocker cover and ultimately, the cylinder head bolts.
• The engine timing will be locked in place using specifically designed pins and locking tools.
• The timing belt will be removed, or the timing chain loosened off and moved off the camshaft sprockets.
• The cylinder head will then be undone in a specific sequence.
• Once all the bolts are out, the cylinder head will be removed and the surface of the engine block and cylinder head will be cleaned of all residue of the old gasket.
• In the case of the majority of cylinder heads, it will need to be pressure tested to ensure it’s structure is sound and then go through a process called skimming. This process ensures that the surface that the new gasket will come into contact with is perfectly flat and clean.
• Once the mechanic has completed the work on the components, the engine is reassembled with a new cylinder head gasket.
• If the engine’s camshaft(s) are driven by a timing belt, this belt will be renewed along with a new water pump if it is on the timing belt circuit.
• Once the engine is back together, the cooling system will be refilled and the oil replenished along with a new filter.
• If the oil has become contaminated with the coolant, an additional oil flush may be required and likewise, if the cooling system has become contaminated, the cooling system will be flushed.
• Once everything is back together, the mechanic will run the engine.
• Finally a road test will ensure that everything works as it should when the engine comes up to temperature and finally any error codes present will be cleared down and re-checked.

As we mentioned previously, this is not a full exhaustive list of what will be done as each engine has its own requirements.

What does this repair cover?

Unless otherwise stated, the quote for your head gasket to be replaced will cover;

• The cost of the parts as listed for your vehicle
• Coming to you
• Removal and cleaning, then taking the cylinder head away for pressure testing and skimming
• Fitting of the parts
• Disposal of the old parts (unless you request to keep them)
• VAT (if applicable)
• 12 months parts and labour warranty

What to search for on the ClickMechanic site?

Cylinder head gasket replacement

How much does it cost to have a head gasket replaced?

The cost of a cylinder head gasket replacement depends on your car and what parts your car's manufacturer recommends.

Find out what you could save by visiting ClickMechanic https://www.clickmechanic.com/jobs/head-gasket-repair

FAQ’s

I have another quote which is quite a bit different than your?

If you are comparing quotations, please ensure that the quotes you have all include the cylinder head pressure test and skimming. Also make sure that if your engine has a timing belt, that they are quoting for its replacement as well.

Not all companies will include these up front, they will add it to the bill after advising you that it needs to be done once they have commenced the work.

Does my cylinder head get tested and skimmed?

Unless specifically stated to the contrary, all cylinder heads will undergo a pressure test and surface skimming. Without doing this, the mechanic cannot be certain that the head is in good enough condition to be reused.

How long will my car be out of action for?

As with all major invasive engine work, these things cannot be rushed. The strip down would be performed on the first day, then there will be a period of 2-4 days while the cylinder head is tested and prepared for refitting, before the final day when it is all put back together.

Replacing a cylinder head gasket is not a simple, same day repair.

Can you reuse my timing belt?

Under no circumstances, no matter how recently it was changed, can a timing belt be refitted. Even the slightest nick in the belt can have a catastrophic outcome within a few miles.

I have only just had my water pump changed?

If your water pump was recently changed as it is driven by the timing belt, then, at the mechanic's discretion, it can be reused.

Will a new timing chain be fitted?

Unless specifically requested as part of the quote, the timing chain and it’s guides will not be replaced.

Can I supply my own parts?

No, we will not fit customer supplied parts unless they are a brand new item, purchased from a dealership with the receipt as proof of purchase. There is no flexibility over this due to insurance and warranty issues.

What happens if the mechanic finds that the head gasket doesn’t require changing and the problem is due to another issue?

In this scenario, the mechanic will provide a no obligation quote for the correct repair. Should you accept this, the mechanic can alter the booking accordingly. If you decide not to go ahead with the alternative repair, the mechanic can change the booking to a call out and diagnostic booking and charge according to the time spent with the vehicle and call out.

Associated repairs

Engine compression test
Cooling system pressure test (leak detection)
Check Engine oil pressure