The head gasket is a critical component beneath the bonnet, providing a seal between the cylinder head and engine block. While it’s quite rare to get a fault in the head gasket, it’s important to know what the signs are so you can diagnose and fix it before it becomes a bigger issue.
In this guide, we’ll be providing a complete overview of head gasket faults, the signs to look for, and how much it costs to replace a blown head gasket.
What is a Blown Head Gasket?
A blown head gasket happens when the seal between the cylinder head and engine block fails. The head gasket seals the combustion chambers (cylinders), oil passages, and coolant passages between the block and head. It doesn’t seal “pistons,” which are moving components inside the cylinders, not something a static gasket seals directly.
When the head gasket fails, these channels are no longer sealed, which can result in coolant leaks, oil leaks or gases escaping from the combustion chamber. A blown head gasket happens when the engine overheats, causing an increase in thermal pressure which puts immense strain on the gasket.
How Long Do Head Gaskets Last?
Head gaskets are usually a pretty resilient car component, lasting about 200,000 miles, which is considered about the lifetime of most cars. That means, if you look after your car and follow the service schedule, you should never be faced with a blown head gasket.
Symptoms & Causes of a Blown Head Gasket
What are the Signs of a Blown Head Gasket?
A blown head gasket shares similar symptoms to other engine faults, including overheating, but there are a few signs that can tell you exactly what you’re dealing with. Below, we list some of the classic things to look for when diagnosing a blown head gasket:
- Thick white smoke billowing from the exhaust. This suggests that coolant/antifreeze and oil are being burned up in the combustion chamber after leaking through a faulty gasket.
- Poor engine performance and rough idling noise. Because the combustion chamber is no longer correctly sealed, this results in the inefficient combustion of fuel and air, leading to a rough idle noise and overall drop in performance.
- Milky coloured engine oil. If the gasket blows to the point where coolant/antifreeze leaks into the oil return passages, you might find that your car’s engine oil appears milky.
- Overheating engine or bubbles in the radiator. This is caused by gases from the combustion chamber escaping into the cooling system, leading to rapid engine overheating and bubbling in the radiator cavity.
- Obvious oil or coolant leaks on the exterior of the car. You might notice a pool of liquid on the floor under where your car has been parked. This happens when fluid drains through a crack or fault in the gasket seal.
Some symptoms of a blown head gasket may be very minor at first, to the point where you don’t notice or can ignore them. But, whenever possible, always get any symptoms checked over by a professional mechanic, as small problems can become very big and very expensive quickly in the case of a faulty head gasket.
What Causes a Blown Head Gasket?
The main cause of a blown head gasket is simply overheating. Car components are designed to work within certain temperature tolerances, so when the engine isn’t being cooled effectively, damage can occur to various components including the head gasket. Incorrect ignition timing can also cause damage over time due to the gasket being exposed to excess pressure.
Troubleshooting a Blown Head Gasket
Can You Drive with a Blown Head Gasket?
It is possible to drive with a blown head gasket, but we wouldn’t recommend it. As we touched on above, small problems like a rising temperature gauge or smoke coming from the exhaust can quickly cause much bigger problems – particularly if coolant/antifreeze gets into the oil.
In the worst-case scenario, you might need an entire engine rebuild or a replacement head gasket if you ignore the symptoms for too long. If you catch it early enough, a faulty head gasket can be repaired without a full replacement, which will not only save you time and money but could also mean the difference between you not having to buy a new car.
It’s important to know the symptoms of a blown head gasket so that you don’t continue driving and cause bigger problems. At the first sign of any problems, always get your car checked over by a professional mechanic who will be able to diagnose the issue and come up with a good solution.
How Much Does It Cost to Replace a Head Gasket?
A head gasket replacement can cost anything from £500 to thousands of pounds depending on the garage and the make and model of your car. It’s one of the most expensive mechanical issues to sort out, which is why a lot of drivers feel forced to send their car to the scrapheap rather than fork out for a replacement – otherwise, it’s a false economy.
The actual head gasket itself is quite affordable. Where costs really start to add up is in the labour. Because the head gasket is seated at the centre of your engine, the work needed to disassemble and reassemble the engine alone can take up to and over 10 hours – so you can see why a head gasket replacement would be so pricey.
Will Car Insurance Cover a Blown Head Gasket Repair?
An insurance company will only pay for a blown head gasket if it is damaged in an accident. Much like brakes and tyres, your car insurance will not pay for a blown head gasket that has been damaged during the general use of your vehicle.
Can You Repair a Head Gasket Yourself?
In some cases, you might be able to repair a head gasket. This is only when there’s a very small leak, which is causing symptoms like overheating and a loss of coolant/antifreeze.
To repair a leaky head gasket, you’ll need to use a sealant. Our sister brand, Holts, produces a professional cooling system leak repair called Wondarweld, which is designed to seal cracks in the head gasket, cylinder heads and engine blocks, for a permanent repair.
Remember, the earlier you diagnose a blown head gasket, the more likely it is that you’ll be able to use a sealant to repair it, without the need for a full replacement.
Head Gasket Preventative Maintenance
As we’ve discussed, blown head gaskets are usually caused by overheating, meaning that proper maintenance is the best way to avoid a costly repair. Regular servicing will replace coolant and ensure that the coolant system is in proper working order. If you spot a puddle of coloured fluid underneath your car (could be green, orange, pink, blue or yellow depending on the type of coolant your vehicle uses), it could be a sign of a leaking radiator or cooling system and will require immediate attention to prevent irreversible damage to the engine.
Regular servicing will check your coolant and top it up as needed, and coolant should be fully replaced at the intervals recommended by your coolant’s manufacturer (this varies from around 2 years for older coolant types to up to 10 years for modern long-life coolants) to keep the cooling system in proper working order.
We hope this guide has been useful in helping you troubleshoot your car’s head gasket. For more how-to guides and motoring features, take a look at the Prestone blog, or for our complete range of engine additives and fuel system cleaners, visit the homepage today.